Sentinel II - History

Sentinel II  - History

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Sentinel II
(MB: 1. 45'; b. 11'6"; dr. 4')

The second Sentinel, a motorboat built in 1918 by Richardson Boat Co., North Tonawanda, N.Y., for the Coast Guard, was completed on 17 June 1918 and assigned to St. Mary's River patrol, Sault Ste. Marie, Mich.

Returned to the Coast Guard when the services were separated on 28 August 1919, Sentinel served until 1935, being renamed AB-I S in 1923.


Power may be supplied by batteries or a permanent AC or DC source, described as follows:

  • 4 x AA size Rechargeable NiMH Batteries (2300mAh) (included)
  • 4 x AA size Alkaline Batteries (not included)
  • USB Port DC 5V Power Supply
  • AC Adapter (AC 120V 60Hz to DC5V 1000mA)
  • DC Adapter (DC 12V to DC5V 1000mA)
  • USB connection to PC for firmware and database updates through Sentinel software

Frequency Coverage

  • 25.0000 - 512.0000 MHz
  • 758.0000 - 823.9875 MHz
  • 849.0125 - 868.9875 MHz
  • 894.0125 - 960.0000 MHz
  • 1240.0000 - 1300.0000 MHz


  • Ability to quickly store CTCSS, DCS, or NAC tones
  • Ability to quickly save a found Unit ID
  • Better location precision for systems – allows you to define a department’s location and range using up to 32 rectangles instead of a single circle (circles are still supported). – sounds a programmable alert when a channel set to alert becomes active. /DCS/NAC tone decode that displays CTCSS tones/DCS codes and NAC codes being received
  • Emergency Alert – sounds an alert when a unit triggers their emergency status (on compatibleradio systems).
  • Instant replay plays back up to 240 seconds (4 minutes) of the most recent transmissions.
    • One-touch recording to capture transmissions for later playback

    Extreme Upgrade Features

  • Complete Front-panel programmability for EDACS and LTR Systems
  • Limit Search and Conventional Discovery modes
  • USB Audio output and control
  • RR System Compatibility

    This scanner is compatible with the following Trunking System Types and System Voices used in the RadioReference Database, of course you must verify that the scanner will cover the appropriate frequency range:

    Sentinel II - History

    The High Standard Sentinel Revolver

    High Standard introduced their Sentinel revolver line in 1955, probably at the request of Sears Roebuck, which was a major customer and owned quite a bit of High Standard stock. Sears wanted a low-cost kit gun or “tackle box” revolver to sell under their J.C. Higgins brand. It was sold by Sears as the J.C. Higgins Model 88 . The J.C. Higgins guns were given distinctive grips, cylinder flutes, and cylinder release pins. Private label versions of the Sentinel were also made for Western Auto (the Revelation Model 99) and Armamex (Colonel Rex Applegate’s company in Mexico).

    The Sentinel was a 9-shot .22 revolver. It was advertised to have an anodized aluminum frame, high-tensile carbon steel barrel and cylinder, single-stroke multiple ejection, a swing-out counterbored cylinder, a movable square-notched rear sight, a non- slip scored trigger, a diamond-checkered grip (though they didn’t mention it was plastic), and target accuracy.

    The innovative design was completed by Harry Sefried, High Standard’s young design engineer, in a mere six months. Sefried wasn’t afraid to incorporate good ideas wherever he found them. The squared-off grip on the first model was modified from the Colt New Model .36 Pocket Pistol of 1862, and one shooter was said to remark that it was “the first decent grip on a revolver since the Civil War.” It remains to this day one of the most comfortable revolver grips I have ever encountered. The simplified cylinder lock design was taken from Hugo Borchardt’s experimental revolver of 1876, which he designed while working for Winchester and which was observed by Sefried during his own five years at Winchester. The gun, like the Broomhandle Mauser, is screwless but for the grip screw.

    These two are R-101 Sentinel revolvers made in 1958.

    The top revolver is an R-106 Sentinel Deluxe from 1965, and beneath it is an R-103 Sentinel from 1961.

    There is an integral thumb rest molded into the frame behind the cylinder housing on each side, making the gun feel quite natural in the hand. The grip section and frame are die cast from aluminum. There is no cylinder thumb release to interrupt the smooth frame or complicate manufacture and assembly. The gun can be broken down into four main component groups: (1) the cylinder and crane, (2) the trigger-guard/grip, (3) the barrel and frame assembly, and (4) the hammer, trigger, and other lockwork components. Everything is held together by the hammer pin, which runs through both the trigger-guard/grip and the main frame. Coil springs are used throughout.

    Sefried designed a unique ratchet mechanism that utilizes nine holes drilled into the rear of the extractor, worked by a traditional pawl that extends from the frame. The holes give the pawl a positive interface, providing flawless cylinder rotation and reducing the machining necessary on the frame and cylinder. The design also reduces wear to the ratchet mechanism that eventually causes problems with more traditional designs. The nine-hole ratchet mechanism was abandoned in later-production Sentinels.

    The Sentinel has an extended forcing cone that nearly eliminates lead shaving as the bullet enters the barrel. I hate it when a revolver spits hot lead out the side when I’m standing next to the shooter--it could be a fatal distraction in a fire fight.

    The Sentinel was originally available in a so-called blued finish (which was actually a selenium black). The nickel finish was available in April of 1956. The early nickeled guns cost $5 or $6 more than the blued guns. The MSRP for the blued gun in 1955 was $37.50. The Sentinel had a one-piece wrap -around plastic grip. Originally the blue guns had a brown grip and the nickel guns had a white grip, but that scheme was not retained throughout production.

    A 1955 catalog says the gun was available with a 3 or a 5 inch barrel. A parts list circa 1957 or 1958 shows 3 inch, 4 inch, and 2-3/8 inch barrels were available. By 1956, a 6 inch barrel was also available. The 3 inch barrel was dropped in 1964.

    Sometime in the second half of the 50’s High Standard licensed the firm Armscor, a subsidiary of Squires Bingham & Co. in the Philippines, to manufacture the Sentinel. I do not know if they imported the parts from the U.S., though I suspect they did and the guns were simply assembled in the Philippines. These gun were not marked with an R-series number. Armscor called it the Model P and the right side of the gun was stamped with P followed by the serial number.

    In 1957 a snub-nose model of the Sentinel was introduced, with a rounded butt on the grip. The early guns had a bobbed hammer, through about 1960, after which they featured a spur hammer. The blued version was Model #9144 and the nickeled version was Model #9145. Color finishes in gold (Model #9161), turquoise (Model #9162), and pink (Model #9163), known as Dura -Tone colors, were offered for the snub-barrel Sentinels. The Dura-Tone guns came in a deluxe presentation case and had white faux ivory grips. In 1967 when the R-108 series began the snub-nose models were given different model numbers, the blued one being Model #9344 and the nickeled one being Model #9345.

    A snubby version was also made for Sears, labeled the J.C. Higgins Model 88 Fisherman, available in blue finish only with a one-piece brown plastic checkered grip and a ‘spur’ on the trigger guard.

    The Western Auto snubby was labeled the Revelation Model 99, available in both blue and nickel finish. The early version with the one-piece grip has a ‘spur’ on the trigger guard, whereas the later version with the two-piece grip has a plain trigger guard

    In 1958 a line of western-style revolvers was spun off the Sentinel line, the first model of which was called the Double-Nine . It was sold by Sears as the J.C. Higgins Ranger Model 90.

    • R-100. The first Sentinel series was called the R-100. The frame carries an eagle logo.
    • R-101. In mid-1956, the hammer and trigger mechanisms were slightly modified for the R-101 series.
    • R-102. In 1961, for the R-102 series, a return spring was added to the ejector rod. On the earlier models, if you didn’t remember to manually retract the ejector into the cylinder before closing you would put a nasty scratch on the left side of the frame.
    • R-103. The R-103 series had slots milled into the ejector instead of drilled holes.
    • R-104. In 1961 the R-104 Sentinel Imperial was issued with a full-sized grip frame, two-piece checkered walnut grips, a ramp front sight, and a target-style trigger. (The regular Sentinel was still available with one-piece plastic grips and blade front sight, and it retained the old R-103 designation.)
    • R-105. These guns were originally made for Sears, but were returned to High Standard when Sears dropped their handgun line in 1963, and were rebranded as High Standard guns (the barrels and grips were replaced). They retain the distinctive cylinder flutes, cylinder pin, trigger guard, and one- piece grip design of the J.C. Higgins guns. As best I can tell, this is one of the least common Sentinels.
    • R-106. In April 1965 the Sentinel Deluxe appeared, with the R-106 series number. The ramp front sight was replaced with a blade, with faux wooden grips. The old Imperial continued in production.
    • R-107. This was also a Sentinel Deluxe. I have been unable to determine the difference between the R-106 and R-107. Externally they appear to be identical, but the part numbers for the frame, grip, trigger, and hammer were all changed..
    • R-108. In 1967 the Snub-nose Sentinel was given a two-piece grip and the R-108 series designation. The frame carries a trigger logo. A few of this series have no frame logo.
    • R-109. The Kit Gun was introduced in 1969 and given the R-109 series designation. This was the first model with a fully adjustable rear sight.
    • MK I and MK IV. In 1974 the series numbers were eliminated and the Sentinel MK I and MK IV were introduced. These guns had optional adjustable rear sights, wrap-around walnut grips, and the first steel frames to appear in the Sentinel line. The MK I was chambered for the .22 long rifle, and the MK IV was chambered for the .22 Winchester magnum. The MK I and MK IV were available with 2 inch, 3 inch, or 4 inch barrels. The Camp Gun was introduced in this same period. It was similar to the MK I and MK IV, but did not have the barrel underlug which shrouded the ejector rod. The Camp Gun came with a standard 6 inch barrel and adjustable sights, and was available in either .22 long rifle or .22 magnum.
    • Steel Sentinel. At some point the Mark I and Mark IV designations were dropped and the steel frame gun was sold as the “Sentinel” with interchangeable .22 LR and .22 magnum cylinders.
    • MK II and MK III. These were rebranded Dan Wesson .357 Magnum revolvers. They were sold from mid- 1973 through February of 1975. There are persistent rumors that High Standard made the Dan Wesson pistols, but they are completely untrue.

    “The First New Revolver in 50 Years,” by William B. Edwards. Guns magazine, June 1955.
    Hi-Standard pistols & Revolvers: 1951-1984, by James Spacek. Self published, Cheshire, Connecticut: 1998.
    Pistols, A Modern Encyclopedia , by Henry M. Stebbins. Stackpole, Harrisburg, Pennsylvania: 1961.
    “The Sentinel Snub 1957-1974” by Mickey Waldinger,
    High Standard Collectors’ Association Newsletter , Vol XVIII, No 3, September 2009.

    Other items of interest at Unblinking Eye Guns

    Copyright 2009-2011 by Ed Buffaloe. All rights reserved.
    Click on the pictures to open a larger version in a new window.

    USGS EROS Archive - Sentinel-2

    The European Space Agency’s Multispectral Instrument on the Sentinel-2 satellite provides global (from 83 degrees north 56 degrees south latitude) 10-meter resolution, multispectral images every 10 days (2015-present).

    Sentinel-2A tile over a portion of Denmark and Sweden (August 6, 2015)
    (Public domain)

    The Sentinel fleet of satellites is designed to deliver land remote sensing data that are central to the European Commission’s Copernicus program. The Sentinel-2 mission is the result of close collaboration between the European Space Agency (ESA), the European Commission, industry, service providers, and data users. The mission has been designed and built by a consortium of around 60 companies led by Airbus Defence and Space, and supported by the CNES French space agency to optimize image quality and by the DLR German Aerospace Centre to improve data recovery using optical communications.

    The Sentinel-2 mission consists of two satellites developed to support vegetation, land cover, and environmental monitoring. The Sentinel-2A satellite was launched by ESA on June 23, 2015, and operates in a sun-synchronous orbit with a 10-day repeat cycle. A second identical satellite (Sentinel-2B) was launched March 7, 2017 and is operational with data acquisitions available on EarthExplorer. Together they cover all Earth’s land surfaces, large islands, and inland and coastal waters every five days.

    The Sentinel-2 MultiSpectral Instrument (MSI) acquires 13 spectral bands ranging from Visible and Near-Infrared (VNIR) to Shortwave Infrared (SWIR) wavelengths along a 290-km orbital swath.

    The MSI sensor data are complementary to data acquired by the U.S. Geological Survey (USGS) Landsat 8 Operational Land Imager (OLI) and Landsat 7 Enhanced Thematic Mapper Plus (ETM+) (Comparison of Sentinel-2 and Landsat). A collaborative effort between ESA and the USGS provides for the public access and redistribution of global acquisitions of ESA’s Sentinel-2 data at no cost through secondary U.S.-based portals, in addition to direct user access from ESA.

    Spectral Bands and Resolution

    The MSI measures reflected radiance through the atmosphere within 13 spectral bands. The spatial resolution is dependent on the particular spectral band:

    • 4 bands at 10 meter: blue (490 nm), green (560 nm), red (665 nm), and near-infrared (842 nm).
    • 6 bands at 20 meter: 4 narrow bands for vegetation characterization (705 nm, 740 nm, 783 nm, and 865 nm) and 2 larger SWIR bands (1,610 nm and 2,190 nm) for applications such as snow/ice/cloud detection or vegetation moisture stress assessment.
    • 3 bands at 60 meter: mainly for cloud screening and atmospheric corrections (443 nm for aerosols, 945 nm for water vapor, and 1375 nm for cirrus detection).

    SENTINEL-2 Radiometric and Spatial Resolutions

    Band Number Central Wavelength (nm) Bandwidth (nm) Spatial Resolution (m)
    1 443 20 60
    2 490 65 10
    3 560 35 10
    4 665 30 10
    5 705 15 20
    6 740 15 20
    7 783 20 20
    8 842 115 10
    8a 865 20 20
    9 945 20 60
    10 1375 30 60
    11 1610 90 20
    12 2190 180 20
    TCI* RGB Composite 10

    *Data acquired after December 5, 2016 include a full resolution True-Colour Image as an RGB (red, green, blue) composite image created from bands 4, 3, 2.

    The USGS Spectral Characteristics Viewer helps users determine which spectral bands work best to identify their features of interest for image interpretation. This tool also facilitates the visualization of the Relative Spectral Response (RSR) of various satellite sensors.

    Processing Level

    The partnership between ESA and the USGS allows for the distribution of Level-1C top-of-atmosphere (TOA) reflectance data. Level-1C processing includes radiometric and geometric corrections along with orthorectification to generate highly accurate geolocated products.

    Data Products

    The USGS Earth Resources Observation and Science (EROS) Center repackages Sentinel-2 products on a per tile basis while preserving the Sentinel Standard Archive Format for Europe (SAFE) format specification, which allows for the distribution of a user-friendly file size that is approximately 650 MB. Each Level-1C product is a 100 km x 100 km tile with a UTM/WGS84 (Universal Transverse Mercator/World Geodetic System 1984) projection and datum. The Sentinel-2 tiling grid is referenced to the U.S. Military Grid Reference System (MGRS). Tiles can be fully or partially covered by image data. Partially covered tiles correspond to those at the edge of the swath. The download package from the USGS includes one file for each of the 13 spectral bands plus metadata. Update: Data acquired after December 5, 2016 are distributed from ESA in a single tile basis with a shorter naming convention and include a full-resolution True-Colour Image. Previously offered Sentinel-2 data in the EROS archive will be replaced as data with the True-Colour Image become available from ESA. Users may see temporary scene duplication in search results.

    Products are available for download in a zip file, which includes image data, quality indicators, auxiliary data, and metadata. Sentinel image data are in Geographic Markup Language JPEG2000 (GMLJP2) format. GML provides the encoding necessary for georeferencing the image. Sentinel-2 data are intended for scientific use within a Geographic Information System (GIS) or other special application software that supports the GMLJP2 format. ESA offers the Sentinel 2 Toolbox, an open source software product, for the visualization, analysis, and processing of GMLJP2 files/Sentinel-2 data and other high-resolution remote sensing data.

    Full Resolution Browse (FRB) images in Georeferenced Tagged Image File Format (GeoTIFF) are also available from the USGS for Sentinel-2 tiles. This product is a simulated natural color composite image created from three selected bands (11, 8A, 4) with a ground resolution of 20 meters.

    All Sentinel-2 data products are provided free of charge to all data users, including the general public, and scientific and commercial users under the terms and conditions prescribed by the European Commission’s Copernicus Programme.

    Coverage Maps

    Coverage Maps indicating the availability of Sentinel-2 products are available for download.

    Additional Information

    Access Data

    EarthExplorer, USGS Global Visualization Viewer (GloVis), or the Sentinel2Look Viewer can be used to search, preview, and download Sentinel-2 data. The collection is located under the Sentinel category in EarthExplorer.

    The current USGS Sentinel-2 archive is only a partial representation of all available acquisitions from ESA. Users should expect some delay before ESA’s acquired data becomes available on USGS systems.

    Students get to experience World War II history up close

    BOCA RATON — More than 300 students from area schools on Friday climbed into the bellies of war birds that won World War II, smelled those engines' grease and hooked their fingers into machine-gun triggers that seven decades ago took aim at enemies.

    But the Collings Foundation's "Wings of Freedom" tour stop at Boca Raton Airport also drew the kind of history that can't be preserved forever.

    "What was it like in the prison camp?" Ethan Stack, 14, of Boca Raton, asked Irwin Stovroff, 92, of Boca, who piloted a B-24 in World War II — just like one on the tarmac Friday.

    During what was supposed to be his final World War II bombing run, his plane was hit and he bailed out over enemy territory. He was taken prisoner by Germans, he said.

    "When you are a captive and taken prisoner, you have to rely on your enemy for everything," Stovroff replied.

    Boca Raton is one of the most popular stops for the Wings of Freedom tour, which invites the public to take a first-hand look at the World War II planes, the B-17, B-24, and P-51, which were a big part of U.S. victory in World War II. Friday morning, though, it was all about experiencing history up close for hundreds of students.

    Just out from the belly of the B-17, also known as the Flying Fortress, Max Silver, 10, of Delray Beach, and Sunand Sujai, 10, also of Delray, were in line to get into the B-24, a plane known as "The Liberator."

    "It's going to be cool," Silver said. "I want to sit in the pilot's cockpit."

    Getting to touch the actual instruments that gunners used had the fifth-graders from Banyan Creek Elementary jazzed.

    "They let you hold the guns on the side," said Isaac Singer, 11, of Boca Raton.

    Shelby Rogerson, a program assistant with the Palm Beach Schools Transition Program at Florida Atlantic University, said that it was an eye-opening experience for her, let alone the dozen students she brought.

    "Just to peek inside these things," she said. "It gives you newfound respect for what these men went through," she said.

    Students also lined up to talk to Stovroff and Daniel Rothfeld, also of Boca Raton. Rothfeld was a radio specialist aboard C-47s that flew in supplies and fuel to American and Australian soldiers in New Guinea, who were fighting the Japanese.

    Rothfeld flew 305 missions before it was all over, he told the students.

    "How old were you when you started flying?" Caitlin Krinsky, 14, who attends St. Andrew's School.


    As machines, Sentinels have been designed solely for combat.

    • Superhuman Strength: A power that a Sentinel naturally has is the ability to lift tons over their head with great ease and fight with the same strength. Two Mark 10 Sentinels were strong enough to tare Colossus in half. One Sentinel could take down Colossus with one hit in head, stunning him on few second on ground. Sentinel was also able to throw him away across room. Sentinel grabbed Colossus with one hand and held him firmly by the fist, immobilizing him. Sentinel alone proved to be equal, if not more powerful than Colossus.
    • Superhuman Endurance: The Mk I Sentinels were built out of a space age polymer, which is very powerful and durable, making the Sentinels very resistant to most of weapons and mutant powers. It is not known what material the Mk X Sentinels are made from, but it is assumed they are made from the same polymer as their predecessors were. It is seen that only Bishop's energy weapons and powerful destruction explosion of the Mk X Sentinel space ship can actually damage or destroy them (Sentinel X at least). Other weapons and powers can only slow them down. Due to that, if they upgrade their armour with some mutant power, they can get additional armour (Iceman, Sunspot) or get near-indestructibility (diamond, rock or Colossus' metal form).
    • Power Mimicry: Although the earlier models didn't possess such an ability, the Mark 10 Sentinel evolved to the point where they can mimic the powers of virtually any mutant they came across. Not just that, they could replicate a mutant's powers, those replicated powers are more powerful than the powers of original mutants. For example, a Sentinel in ice form could successfully move towards Sunspot without trouble, and shut down/freezing with one hand. A Sentinel in heat/lava/Sunspot form could successfully break Iceman's ice, holding him for neck and crushing his head off. In this form, it could melt treasury's heavy door in seconds. A Sentinel in metal form taken from Colossus could kill Colossus himself in just two hits in head. After the first hit, the Sentinel ripped off Colossus' hand. This is because all mutants powers are upgraded to the human body, while the Sentinel's copied powers are upgraded to this very durable material which Sentinels are build from, so they can create more powerful abilities, making Sentinels invulnerable in some cases.

    Sentinels are also seen to morph into rock forms (probably mimic Darwin's rock form), gaining extreme durability, more weight and immunity to sunspot's heat energy streams. In such forms, while they miss Sunspot with their hands, the Sentinels hit the ground, making it explode, demonstrating very increased strength.

    Another Sentinel under Sunspot's attack is seen to morph into diamond form, mimicking Emma Frost's diamond form, upgrading to his own powerful armor, making him immune to. sunspot's energy heats too. In this form he could create diamond spike which was cut off sunspot's hand.

    • Flight: Sentinels were designed with thrusters within their foot allowing them to defy gravity. By the year 2023, the mark 10s were designed with hover devices enabling them to fly on their own without jet thrusters.
    • Athletics / Agility: Sentinels are seen to be very agile, they could do somersault forward and backward in air and were able to jump at higher distance. They are seen crawling over walls in Chinese monastery (one was climbing up, and few were climbing down)
    • Shape Altering/Weaponizing: Thanks to Mystique's shape altering power, Sentinels are also seen to be able to alter their forms to fit variety of purposes:

        They could become smaller/larger, as explained by developers. This also could be seen in first scene when transporters began to open doors and launching down Sentinels one by one. Those Sentinels did not have hands and legs, perhaps because so more Sentinels could fit into transports.     They also could extend their arms into long and extremely sharp spikes capable of breaking though concrete walls and stabbing/cutting mutants. (Sentinel cut off Sunspot's hand, another Sentinel were impaling and killing Sunspot in his lava form with long claws coming out of each finger).     Before first battle against X men, Sentinels were drilling though concrete walls with powerful drills. It took few second until they break though concrete, then almost immediately drills converted back into hands.

    • Immunity to certain weapons: As robots, Sentinels are immune to psychic attacks from Xavier and other telepathic mutants. They are built out of a space age polymer, making them immune to Magneto's control. They have X-Gene detector to detect mutants from very long distance, which means that shape changing mutants like Mystique cannot fool them disguising into humans.


    Sentinels have evolved since their creation in the 70s and therefore have utilized a variety of different weapons along the way.

    Completion lymph-node dissections at the time of the primary operation was found to improve local disease control as well as aiding in prognostication. There was no increase in survival from melanoma in patients with sentinel node metastases.

    Melanoma is staged at the time of its surgical excisions using a sentinel lymph node biopsy (SLNB). This minimally invasive technique is performed with methylene blue dye and/or lymphoscintigraphy with intra-operative gamma probe analysis. SLNB is important in the prognostication of melanoma. Clinically in patients with positive SLNB a completion lymph node dissection (CLND) is performed at the time of the SLNB with the goal of local disease control. These patients may also receive adjuvant medical therapies. There is currently no evidence regarding the utility of immediate CLND. This procedure is not without risks, specifically including infection, seroma, wound separation, and lymphedema. [1]

    The Multicenter Selective Lymphadenectomy Trial-1 (MSLT-1) confirmed that SLNB is an important part in the treatment of patients with melanoma. [2] [3] [4] . The MSLT-1 trial demonstrated that pathologic analysis of sentinel lymph nodes was the most important factor for prognostication of melanoma, and that patients who had a sentinel lymph node biopsy had a decreased rate of recurrence of melanoma when compared to patients who had wide excision with no nodal biopsy. Sentinel lymph node biopsy was found to be associated with improved 10 year melanoma specific survival (62% Biopsy with nodal involvement vs 41.5% observation with nodal involvement, P = 0.006) as well as 10 year distant disease free survival (54.8% Biopsy with nodal involvement vs. 35.6% observation with nodal involvement, P=0.002) in patents with intermediate-thickness melanoma (1.2-3.5-mm Breslow depth).

    The MSLT-2 trial demonstrated that CLND offers local disease control, but does not increase disease-specific survival rates in patients with melanoma with sentinel lymph node metastases.


    Cruiser Tank Sentinel AC III

    A total of 65 Sentinel Tanks were produced. 4 variants were produced

    • Sentinel AC I: Mounted the Ordnance QF 2-pounder
    • Sentinel AC II: Upgraded Sentinel AC I
    • Sentinel AC III: Mounted a double barrel Ordnance QF 25-pounder guns
    • Sentinel AC IV: Mounted the Ordnance QF 17-pounder gun

    Characteristics [ edit | edit source ]

    A Sentinel-class shuttle carrying a container

    Designed by Sienar Fleet Systems in the shape of its cousin, the Lambda-class T-4a shuttle, this larger, more spacious shuttle was primarily used to ferry a complement of 75 stormtroopers into battle Ζ] 󈠇 more troops than the Lambda-class. ⎗] The ship featured three wings: one stationary center foil and two articulated flanking wings. Ώ] The landing craft also had shielding strong enough to be able to withstand several hits from a Quasar Fire-class cruiser-carrier's turrets. ⎘] They could also be modified with special containers carrying vehicles. ⎙] The shuttle also had two spotlights at the front of the craft. ⎚] The shuttle had several entry points including a front ramp, a rear ramp, ⎛] and doors to the side. ⎜] The interior of the ship had a main passenger section and a cockpit. In the passenger/cargo area, there were benches and harnesses on each side with a ladder to the side of the front ramp leading directly to a hatch for cockpit access. The cockpit section had four seats. ⎛] The shuttle could also feature a refresher on the opposite side of the ladder. ⎝]


    My first piece on the ancestry of the RQ-170 Sentinel, America’s secret unmanned stealthy sensor truck of choice, got a lot of traffic and was the topic of one of my recent colorful interviews on John Batchelor’s national radio program ( Yet after writing the piece something about the genesis of the now infamous bat-winged tactical reconnaissance platform sat odd with me. I had heard of its unique mission requirement somewhere along the abstract timeline of aerospace technology I have built-in my head over the years, long before even the whole TIER3- concept officially existed. In fact this machine even predated Operation Desert Storm and the rumblings about the possible existence of a TR-3A “Black Manta” like stealthy manned tactical loitering reconnaissance aircraft that surfaced during the late 1980s and hit a crescendo after the first Gulf War. Then it hit me, Northrop’s enigmatic “Whale,” yes, that was it! The progenitor of the USAF’s TIER3- requirement of the mid 1990’s, and thus the resultant RQ-3 Darkstar which subsequently lead too the RQ-170 Sentinel, was most definitely the humble yet intriguing “Tacit Blue” program that dated back to the dawn of the stealth age. After much investigation I realized that by understanding Tacit Blue we can understand it’s grandchild, the RQ-170 Sentinel, better than ever before.

    America’s “stealth revolution” took place in the mid 1970’s, spawned by advances in computer processing and aircraft manufacturing techniques, as well as the ongoing Cold War. By the turn of decade multiple “low observable” programs, spearheaded by a variety of manufacturers, were well underway. Most notable of all of these programs was Lockheed’s notorious bleeding edge “Skunkworks” design house’s “Have Blue” demonstrator, aka the “Hopeless Diamond.” The successful Have Blue program would eventually morph into the world’s first true “Stealth” production aircraft, the infamous F-117A Nighthawk Stealth Fighter (the Nighthawk was really an attack aircraft but marketing is a powerful thing even in the Pentagon’s black budget world). Yet another smaller, less glamorous, but arguably as influential top-secret technology demonstration was also underway around this same period in time, known ambiguously as “Tacit Blue.”

    The Tacit Blue aircraft, known affectionately as “The Whale” amongst those who were involved with the program over at legendary aerospace manufacturer Northrop, had an entirely separate set of objectives than Lockheed’s proposed stealth attack aircraft, although radar invisibility was one they both had in common. Whereas Lockheed, leveraging its innovative “ECHO1” radar predictability software, found the “faceted,” diamond like structural approach suitable for a stealth tactical attack aircraft, where speed and agility were on the requirement list, a few years later Northrop would take an almost entirely opposite route to achieve groundbreaking “low observable” results.

    In the late 1970’s the DoD’s Defense Advanced Research Projects Agency (DARPA) was working hard at breaking open stealth technology’s virtual “Pandora’s box,” and diligently figuring out new ways to leverage the still very young and emerging capability. Never before could America actually build an invisible warplane, and the creative minds over at the Pentagon were deciding exactly where this new revolutionary method of designing aircraft could make the most impact. One of the areas where they wanted to push the stealth envelope was in the business of battlefield reconnaissance. At the time, tactical aerial intelligence was collected via fighter jets, or other very un-stealthy aircraft, that were fitted with cameras and sent out to make daring runs, sometimes at very low-level and at very high speeds, over enemy territory. At best these systems could capture a snapshot in time of the enemies force posture, which could never be exploited in real-time, and was only gained at incredible risk to the aircrews involved. Other strategic surveillance assets, such as the SR-71 Blackbird and especially reconnaissance satellites had similar, if not even more severe drawbacks, as the information they gathered was momentary in nature, and resolutions were at times inconsistent. With these limitations in mind, DARPA hired the Northrop company to answer a simple question: Could emerging “low observable” aircraft technology be used to build an aircraft that could survive while loitering for hours at a time deep behind enemy lines, all the while collecting real-time battlefield tactical intelligence that commanders could exploit in real-time, while being located safely behind friendly lines?

    During this same period of time the USAF was looking to develop an aircraft that could take advantage of recent air to ground radar technology revelations. The concept behind such emerging capabilities was to use a large phased array radar, mounted on an airplane, to provide real-time Ground Moving Target Indicator (GMTI) intelligence. GMTI is a radar mode that basically sees the movement of vehicles across large land masses, as well an associated Synthetic Aperture Radar (SAR) mode that could theoretically map the battlefield using high-resolution radar beams and computer processing instead of optical photography. Both modes are able to peer through inclement weather with ease, can be implemented at long-range, and are persistent in nature. In other words, they can be used to survey enemy territory for long periods of time, looking for not just targets but operational trends in the enemy’s force posture, under almost any conditions. This new radar technology development program was known as “Pave Mover,” and it would prove to have drastic effects on the future of airborne intelligence collection.

    With the “Pave Mover” radar concept and Northrop’s stealthy and persistent tactical intelligence aircraft in mind, the folks at DARPA decided to combine the two into a top-secret program now known officially as the Battlefield Surveillance Aircraft-Experimental (BSAX), code name “Tacit Blue.” By combining the deep penetrating radar capabilities of “Pave Mover” and Northrop’s stealthy surveillance platform, commanders would theoretically be able to look deeper into enemy territory than ever previously imagined, and the products of such a capability could truly be war winning. The only problem would be, how would Northrop engineers leverage a new design philosophy that was still in its infancy to be able to carry a massive radar array while staying invisible to radar at the same time? Further, how would they ensure that the radar itself was not detected through its high power emissions? The program’s goals were truly groundbreaking and in being so they were also incredibly challenging. Literally, the BSAX had to not just blaze a single trail, but many in order to be successful.

    Around the turn of the decade, Northrop had designed an aircraft that was so ugly that it had to be genius, and it was. Resembling a whale, including its blow-hole on top (the jet air intake!) the Tacit Blue was a marvel of function over form. Instead of using the faceted, almost diamond like approach to designing their stealth aircraft, as Lockheed had done a couple of years prior, Northrop engineers took a different approach, one of continuous curvatures, chined edges, and masked vulnerabilities. Much of this design philosophy was demanded by the “loiter” part of Tacit Blue’s mission requirements. The aircraft had to feature “all aspect stealth,” whereas an aircraft like the F-117 could be optimized for front and rear, or “coming and going” stealth aspects, as their mission was sneak inside a defense network, drop bombs, and high tail it out of danger. Tacit Blue had no such luxury as it would have to loiter for hours over enemy territory, and thus every angle would be susceptible to radar surveillance for prolonged periods of time. Tacit Blue’s rounded approach to stealth, known as curvilinear design, would be a massive development that would affect future stealth technology arguably more than the famous F-117’s “faceted” approach to masking radar signatures.

    The Tacit Blue Weighed in at some 30,000lbs, measured around 55’X55′ and looking more like a motor-home than an aircraft. With a massive phased array radar, provided by Hughes, shoehorned into its boxcar fuselage, the ugly Whale was one unaerodynamic flying creature. It’s surfaces were so smooth that it almost took on a sculpted appearance. This does make some sense as one of its main designers actually sculpted its unique fascia while sitting on a park bench after being stumped on how to come up with a solution for DARPA’s BSAX challenge. By its very nature, Tacit Blue was a highly unstable design and thus had to utilize an advanced fly-wire-system similar to the one used on YF-16. Making the aircraft even more awkward, the design team utilized many parts from existing aircraft to minimize design time, complexity and cost. At a price tag of about $130,000,000 to build, with a total program cost of about $170,000,000, the Whale was an expensive ugly duckling, but it would pay for itself in spades over some 135 test flights between 1983 and 1985.

    During these 135 test flights Tacit Blue and the whole BSAX team would not only pave the way for a multitude of stealth and surveillance technologies, but in doing so it would make the exact case for a TIER3- unmanned stealth and persistent tactical reconnaissance requirement that would spawn the RQ-3 Darkstar some ten years later, and eventually the RQ-170 another decade after that. In many ways Tacit Blue was the manned experimental RQ-170 of decades past. Here are some of the key BSAX program’s accomplishments:

    1.) “Curvilinear” and “All-Aspect” Stealth- Tacit Blue’s design was incredibly unique for its time, and many, if not all of its features can be seen today on modern stealth aircraft and UAVs. Its continuously curving architecture was revolutionary and would pave the way and help validate the design for Northrop’s B-2A Bomber, still America’s most valuable (that we know of) deep penetrating weapon system some 20+ years after it’s unveiling. Also, the “Whale’s” exact design was almost exactly copied for the Tri-Service Standoff Attack Missile (TSSAM), although the program was cancelled in 1993 due to budget and technological reasons, similarities are still abundant on the JASSM missile system currently in service. Its chined forward fuselage bears a close family resemblance to that seen on the YF-23, and it’s elliptical exhaust can be identified on the RQ-170 Sentinel. It’s overhead stealthy jet inlet, and deep buried motors are both concepts utilized to a great degree on the B-2 and RQ-170 as well.

    Tacit Blue’s “all aspect” stealth design philosophy has been used in almost every low observable product in existence today and can be seen extrapolated to a greater, more refined degree on the f-22 and F-35. In fact the “curvilinear” design method, aided by much more powerful computer aided design software and processors, would allow stealth aircraft to be configured more freely for many different kinds of missions and uses as compared to the F-117’s inefficient and limiting faceted architecture. Although the Tacit Blue’s design was so ahead of its time it seems as if it is still being used today with minimal modifications. Case in point is General Atomics’s new Predator C, also known as the Avenger, which possesses and uncanny resemblance to Tacit Blue some 25 years after its last flight. In summary, structurally alone, the Tacit Blue changed the way America builds aerial weaponry forever, arguably more so than the more popular “Have Blue” demonstrator and it’s infamous F-117 successor.

    2.) Infra Red Heat, Noise, and Optical Signature Reduction- It is said that the Tacit Blue was literally the coolest aircraft ever tested at the time. The aircraft ejected its exhaust before and above the end of aircraft’s tail section. This made the motor’s direct heat signature masked to anyone viewing the aircraft from below. It is also said that Tacit Blue’s exhaust was “after cooled” or chilled after being ejected from the aircraft’s engine, and this, combined with chemicals injected into the exhaust, all but eliminated the possibility of creating a contrail or being detected with infra-red sensors. Further, its light paint was optimized for medium and high altitude operations during daytime, and its deeply buried motors made the aircraft incredibly quiet. All of this and of course the unlikely overall shape of the Tacit Blue would make the aircraft almost entirely undetectable. These low-signature revelations would be exploited in advanced military aircraft design for decades after the Whale’s last flight.

    3.) Low Probability Of Intercept (LPI) Radar- The Tacit Blue’s design was extremely stealthy, but packing a huge radar that emits tremendous amounts of energy over or near an enemy battlefield is not stealthy to say the least. Passive detection devices and Electronic Support Measures (ESM) could alert the enemy to the BSAX’s whereabouts almost as easily as radar detection if it’s radar were to be employed in a normal fashion. So engineers from Hughes and Northrop worked on cutting-edge ideas to make what was already a breakthrough radar technology, that being Ground Moving Target Indicator (GMTI) capability, all that more revolutionary by making its electronic emissions almost impossible to detect by the enemy.

    LPI radar works using a variety of tactics that combine collectively to lower the possibility of a radar being detected while turned on. Advanced methods such as utilizing agile frequency modulation over a very wide band, emitting a much more finely tuned beam at lower power for short bursts instead of long continuous emissions, all via a phased array radar design that is paired with advanced back-end computing power fantastically lowered the chances of the Tacit Blue being detected via its emissions. Today LPI radar techniques, especially when joined with new Active Electronically Scanned Array (AESA) radar sets has changed the way radar is used in aerial and sea combat. The technology was most certainly used in the ATB program which produced the B-2A Spirit that was fielded just a few years after the Whale made its last flight. At the time the B-2 was a fantastic asset to migrate LPI airborne radar technology into because it had massive real estate on it’s leading edge for a pair phased array radar arrays to be installed, and it could utilize them while under it’s stealth cloak. Today, stealth fighters like the F-22 and F-35, and even modern combat ships use advanced LPI radars to their advantage, allowing them to keep tabs and engage their enemies while maintaining a high degree of invisibility. Further, the exact LPI and GMTI technology pioneered by Tacit Blue, improved and miniaturized over time, most likely makes it possible for the stealthy RQ-170 Sentinel to penetrate deep into enemy territory and actively gather high-resolution radar intelligence without being detected. This has been further confirmed by Pentagon officials in a recent piece posted over at Aviation Week where sources said that the RQ-170 started out as a radar platform and then was refitted for electre-optical streaming video as well a few years back.

    4.) Data Links: Unlike Tacit Blue’s larger, standoff oriented successor, the Boeing 707 based E-8 J-STARS, which emerged as the chosen production platform as a result of the multi-tiered “Pave Mover” demonstration program, Tacit Blue had no radar and intelligence support operators on-board. Seeing how the requirement for real-time intelligence was a key part of the “Pave Mover” program and thus the BSAX program, engineers had to figure out a way to not only control the radar but also broadcast the stealthy Tacit Blue’s intelligence data back to operators on the ground for immediate exploitation. This was a massive departure from airborne intelligence collection of the day, which either saw large airframes utilized so that operators on-board could control the surveillance systems and utilize the information collected, or smaller airframes would be utilized to go out and collect intelligence that could only be leveraged once deciphered by specialists well after the mission ended. The incredibly high-risk nature of a deep penetrating, loitering, airborne surveillance platform’s mission set could be somewhat offset by relocating the radar operators and intelligence professionals off the aircraft and far behind friendly lines. These operators would be connected to the small stealthy airframe via a data link. Without breakthroughs data link technology Tacit Blue’s objectives would have been virtually impossible to achieve.

    Tacit Blue used line of sight data links that were also low probability of intercept in nature and thus difficult to detect by the enemy. All the data collected over “enemy” territory was transferred back to the control station it was “tethered to,” theoretically far away from the front lines of the battlefield. At the time data links were used mainly between air superiority fighters to sort targets and to provide other situational awareness functions that would help crews be less reliant on radio communications, or in TV guided weaponry like the “Popeye” series of missiles. Tacit Blue stepped way beyond this capability and truly blazed the way for modern UAV technology and their related ground control and information exploitation concepts as we know them today. Most notably those used to satisfy the TIER2+ (which became the RQ-4 Global Hawk) and TIER3- (which became the RQ-3 Darkstar) requirements put forth by the USAF almost a decade after the Tacit Blue took its last flight. Today, data links, and LPI optimized data links, are used in almost every combat aircraft flying in the US’s inventory. These links primarily exist in the form of the Multifunctional Information Distribution System (MIDS)/Link-16 architecture. Further, a new data link optimized for stealth aircraft, which utilizes cutting edge LPI technology, is currently under development. This system is known as Multifunctional Advanced Data Link (MADL) which will be fielded on America’s stealth F-22, B-2, F-35 and Next Generation Bomber force. Modern data links have been described as the most game changing weapon system of the 21st century, and offer a single pilot a gods eye view of battlefield around him, with massive amounts of data being fused into a single tactical picture right at his or her fingertips. Never before has such a widespread capability existed, and it is arguably the most significant “force multiplier” concept combat aircraft have seen for decades.

    5.) Ground Moving Target Indicators (GMTI) Radar Technology: As the deeply classified arm of the “Pave Mover” program, the Whale proved that such technology could be shoehorned into a relatively small tactical asset, when paired with a tethered ground station, and this aircraft could also be invisible to radar, loiter for hours in denied air space, peering deeper into enemy territory than a standoff asset could, literally into a foe’s vulnerable rear echelons. The testing done with Tacit Blue no doubt added greatly to the E-8 J-STARS program, and was further leveraged in the RQ-4 Global Hawk over a decade later, of which GMTI capability was one of the main capability requirements. It is also widely speculated that the RQ-170’s original mission was to provide high resolution Synthetic Aperture Radar (SAR) pictures and possibly GMTI data back to commanders on the ground to be used in real time. GMTI is not only effective at tracking armored columns, but it is also effective at cataloging critical “pattern of life” intelligence data in and around a target area. Since Tacit Blue flew with it’s mini-van sized Sideways Looking Aerial Radar (SLAR), such radar technology has been miniaturized to a massive degree. These radars can now be packed inside the dimensions of a targeting pod, while offering much more capability, and have become ideal for UAV operations.

    6.) Dual-Role, Stealthy Electronic Intelligence (ELINT) Concept: Although the Tacit Blue may never have flown with passive ELINT hardware on-board, those involved with the program have made it clear that they were very aware of the “Whale’s” unique potential for carrying automated electronic listening equipment to passively collect the enemy’s electronic order of battle and their communications without them ever knowing. This ELINT suite of equipment could be manipulated and it’s products exploited in real-time by the ground control station just like the radar array. This information could then be used to great effect for Suppression of Enemy Air Defenses (SEAD) and general intelligence purposes. In other words, Tacit Blue could provide similar functions as the much larger, standoff in nature RC-135 “Rivet Joint,” as a secondary mission while conducting radar surveillance. Since the aircraft was already being theoretically risked over enemy territory it was only logical that such a risk be leveraged to its maximum potential in order to gain the maximum amount of rewards. This “cherry on top” added capability is very similar to what we know about the F-22 and it’s ALR-94 ESM kit, which some say is the most potent part of the Raptor weapon system, and supports what many hypothesize about the RQ-170, that it has a secondary ELINT capability built-in.

    7.) Advanced Fly-By-Wire: The malformed Tacit Blue was unstable in both pitch and yaw and depended on a quadruple redundant fly-by-wire system in order to literally keep its nose pointed in the right direction. The aircraft was proven to flip on its back and weather-vein tail first into the airstream during wind tunnel tests! It has been said that the Whale was the most unstable aircraft mankind had ever flown at the time, a situation fraught with danger and pitfalls. Yet engineers were able to refine the flight control system enough so that the aircraft would fly reliably, although it was in no way a hot rod or high-performance machine. Lessons learned during the design and implementation of the “Whale’s” flight control system would be used later on as aircraft designs became more function over form. Thus opening up the opportunity to fly aircraft of strange, inherently unstable shapes, such as the B-2 flying wing bomber, and later the RQ-170 Sentinel. In the end, and against great odds, Northrop built an invisible sensor truck, and a flyable one at that.

    As you read through the incredible accomplishments of the Tacit Blue / Whale / BSAX or whatever you want to call it, there can be little doubt that this aircraft was the progenitor of the TIER3- program, and thus the RQ-170 Sentinel as we know it today. The BSAX program definitively marks the first time in aerospace history where such a concept was envisioned, tested and validated. Additionally, as part of the decision to fund the Tacit Blue program, the USAF had a strong interest in utilizing the technology for an unmanned aircraft, a concept that was really beginning to emerge as the possible future of air combat at the time. Tacit Blue’s mission, persistent tactical reconnaissance over enemy airspace, is a very risky one. By taking human risk out of the equation the concept could be more readily applied during a time of conflict and the USAF knew this, although the technology to make such a capability reality simply did not exist at the time.

    Almost everything we know about the TIER3- program that emerged in the mid 1990’s and the subsequent RQ-170 Sentinel that sprang from its ashes can be traced directly to Tacit Blue. It’s curvilinear low observable design was utilized extensively on the B-2 and can be seen leveraged to even a greater degree on the RQ-170. The same can be said for the RQ-170’s overhead inlet, deep buried motor and light paint optimized for daytime operation. Even the exhaust of the RQ-170 matches that of the Whale’s to an uncanny degree. Then there is the Tacit Blue’s data link systems, cutting edge at the time, that now represents the genesis of all unmanned aerial vehicles control interfaces. In effect the offspring of the Tacit Blue’s ground control stations and data links would make the unmanned aircraft concept as we know it today actually feasible. By the 1990’s breakthroughs in computer automation and satellite communications would let unmanned aircraft dream become a reality.

    Low probability Of intercept surveillance radar and advance data links would make it so the RQ-170 could penetrate deep into enemy airspace and operate for hours without a high risk of being detected by passive listening systems. Even the proposed secondary ELINT capability of the BSAX is almost certainly on-board the RQ-170. Beyond logical deduction there were multiple reports from sources in the Pentagon that the RQ-170 not only transmitted real-time video on the night of the Bin Laden raid but that it was also providing key ELINT information so that commanders could monitor the Pakistani’s response, or lack thereof, at critical times during the fragile operation. Even the concept of using an aircraft as a sensor platform only, and communicating its collected data back to a ground station in real-time for interpretation, was the forerunner of the RQ-170’s real-time tactical reconnaissance capabilities.

    The definitive proof that establishes a direct ancestral link between Tacit Blue and the RQ-170 Sentinel can be found in the very reason why the BSAX was created in the first place, to prove that a small stealthy tactical intelligence platform could loiter for long periods of time over denied airspace undetected, all the while transmitting its high fidelity intelligence back to commanders on the ground in real-time. Does this sound familiar? Of course it does, as this is the exact same unique mission requirements as the unmanned TIER3- concept that emerged almost a decade after the Whale’s last flight. Further, the BSAX was really a minimally manned asset, the pilot providing the flight control only because remote systems were simply incapable of doing so at the time, and were not needed in order to prove the concept during controlled tests. So although the larger 707 based E-8 J-STARS become the known winner of the “Pave Mover” program, the idea of a stealthy and persistent tactical surveillance aircraft was proven by Tacit Blue with flying colors. Further, it was realized that by simply replacing Tacit Blue’s radar, or in addition to it adding advanced imaging equipment, you would have an asset that would be almost entirely undetectable and capable of collecting multiple forms of intelligence during its high risk missions.

    It would take a decade for satellite data links and computer hardware to catch up with the BSAX in order to make the concept an unmanned reality. Even the TIER3- requirement of the early 1990’s stated the need to leverage miniaturized LPI radars as part of the program, along with fully passive electro-optical surveillance payloads. And from the TIER3- minus requirement, and the program’s resulting RQ-3 Darkstar, the RQ-170 Sentinel was born, as was detailed in my prior piece linked above. So the Sentinel’s direct lineage, its exact reason for existing, dates back some 30 years to the birth of the BSAX program and Tacit Blue.

    In the end the RQ-170’s pedigree is a long one of secret successes and public failures, culminating in a drone so effective and so critical to national security that it was used on the most sensitive American mission since the Doolittle Raid on Japan at the beginning of WWII. The fantastically successful Tacit Blue demonstrator, the clear father of the troubled Darkstar, the grandfather of the history making Sentinel, and the uncle of so many other successful aircraft that used smaller parts of its innovative technologies to accomplish their own diverse missions, leaves a legacy that is truly stunning. Yet one question does emerge out of this epic family saga: After learning so much about the success of the Tacit Blue, did this aircraft and it’s mission set in fact go the way of the RQ-3 Darkstar, being evolved into a more operational form under a dark classified cloak? Even the Tacit blue took over a decade from its last flight to become partially declassified. What is to say that a follow-on, much more capable system was not fielded once the BSAX technology demonstration program shutdown? Just as the standoff oriented “TIER2+” RQ-4 Global Hawk was pursued in the white world and the “TIER3-” RQ-170 was pursued in the black, maybe the similarly standoff oriented E-8 J-STARS and a stealthy tactical Tacit Blue follow-on blazed a similar path? Isn’t this more probable than not when compared to historical patterns of evolution regarding such programs and game changing capabilities?

    Was Tacit Blue’s first actual offspring the fabled manned TR-3A “Black Manta” that was spotted around the globe, supposedly assisted the F-117A over Baghdad, and possibly crashed at Royal Air Force Base Boscombe Down in the 1994, or an aircraft similar to it? Only a couple of months after this mysterious crash at Boscombe Down of an aircraft that fits the proposed tactical manned stealth reconnaissance aircraft mold, the SR-71 program was reactivated against huge odds. Regardless of any speculative details it just seems somewhat apparent there may in fact be a manned missing link in the RQ-170’s murky family tree. Something existing between the Tacit Blue technology demonstrator and the TIER3- unmanned requirement of the mid 1990’s seems like almost a given considering the historic continuity of such programs. Or are we really to believe that the USAF, after the conclusion of the Tacit Blue program, with such an innovative and proven tactical battlefield intelligence technology in hand, decided not to pursue a follow-on in any form until the curious announcement of the TIER3- program that resulted in the still-birth of Darkstar in the mid 1990’s? Was there really no aircraft to fill this role, even in very small numbers, between the triumphant Tacit Blue’s last flight, and the far-reaching unmanned TIER3- program? Would the existence of such a craft in fact also provide an answer to the odd SR-71 Blackbird retirement initiative of the late 1980’s?

    The SR-71 was designed during a time when true stealth was a pipe-dream and thus it had to leverage high altitudes, great speed, and some rudimentary low observable techniques to survive. It would make sense that once the proverbial stealth genie was out of the bottle there would be no need for hugely expensive ultra high-speed reconnaissance over enemy territory. In fact a theoretical aircraft like the TR-3A that utilized subsonic, and/or moderate super-cruise operating speeds while at medium altitudes, and offered near radar invisibility, could actually possess an advantage over one that utilized blistering high speeds and altitudes. Slower speeds would give the platform more time to soak up intelligence data while remaining undetected, and if need be, like the Tacit Blue, it could loiter for long periods of time over denied territory. Did this reasonably faster, more capable and survivable offspring of Tacit Blue nicely fill the gap, along with modern strategic satellite reconnaissance, left by the retirement of the SR-71 Blackbird? One that not only inhabited Tacit Blue’s unique mission set and exploited it’s groundbreaking innovations, but also one that incorporated some of the innovations applied to the B-2 bomber, and the technologies that were publicly showcased during the Advanced Tactical Fighter (ATF) program in the form of the YF-23, although a few years prior, while they were still under a dark shroud of secrecy? Was this in fact Northrop’s ASTRA (Advanced Stealth Reconnaissance Aircraft) that was rumored to exist during the time period in question? It sure makes a lot more sense than the almost mainstream obsession with the possible existence of the “Aurora” high-speed, high altitude spy plane, that would have been unbelievably expensive to develop and operate, while only furnishing similar capabilities than those of spy satellites that the DoD and US intelligence apparatus has already invested in heavily.

    If you asked me my opinion on this a month ago I would have said it would be anyone’s guess, but after the hours of research on the RQ-170’s lineage, it would appear that there is indeed an aircraft flagrantly missing from its family tree. Some 10+ years would have gone by between the time that this invaluable capability was proven and when we would see a public requirement from the USAF to fill such a role in the guise of the unmanned TIER3- program. But was the TIER3- the first attempt at an operational stealth tactical reconnaissance capability, or was it set in place to replace an aircraft that already existed, its main weakness being that human beings were at risk in the cockpit?

    I believe that the BSAX did in fact result in a semi-operational manned airframe of a different configuration, but one of the exact same mission, that leveraged both Tacit Blue, and it’s emerging B-2 cousin’s technology innovations. Such an aircraft would help more evenly fill the gap left by the aging and vulnerable SR-71s on a tactical level, leaving satellites for the strategic reconnaissance mission. Theorizing freely, possibly this program never reached its full potential and was abandoned after a fatal crash at RAF Boscombe Down in 1994, thus ushering in the Blackbird as a stopgap and the TIER3- as a final replacement.

    Like so many things that prowl the skies high above the central Nevada desert, we may never truly know their whole story, although we can apply logic, patterns in aerospace development, known facts and liberal creativity to create a story that is more probable than possible, and probably more believable than the actual truth….


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