Category: Cold War US Light Tank Prototypes

United States of America (1977)
Light Tank – 1 Prototype Built

The High Survivability Test Vehicle Lightweight (HSTV-L) was a light tank testbed created during the late 1970s as part of the Armored Combat Vehicle Technology (ACVT) program. Developed alongside the High Mobility and Agility (HIMAG) testbed, the HSTV-L was designed to operationally test the concept of using speed to enhance a vehicle’s survivability instead of armor. It was also used to test a number of emergent tank technologies, chief of which was an automatic main gun. Only one HSTV-L testbed was produced and saw testing up until the mid-1980s.

History and Development

Initiated in the late 1970s, the ACVT program was a joint venture between the US Army and US Marine Corps (USMC) which would explore concepts for future armored fighting vehicles, with a heavy emphasis on lightweight vehicles. A variable parameter testbed, the HIMAG-A, was the first concept vehicle developed for this portion of the program. It featured an adjustable hydropneumatic suspension system, a 75 mm gun with a sliding breech, and an AVCR-1360 diesel engine coupled to an X-1100-H transmission. Horsepower was variable between 1,000, 1,250, and 1,500 horsepower. This was followed by the HIMAG-B, which was designed to test supine (semi-reclining) crew positions.

In July 1977, AAI Corporation and Pacific Car and Foundry Company submitted proposals for the HSTV-L portion of the program. The HSTV-L would investigate the operational merit of a light tank that could be transported by helicopter, could use a rapid-firing cannon to destroy future armor threats, and could use quick bursts of speed in conjunction with its low profile to ensure survivability. The Pacific Car and Foundry proposal featured a 75 mm ARES gun in an elevating mount with a coaxial 25 mm Bushmaster cannon. It was to be powered by a General Motors 8V71T diesel engine paired with an HMPT-500 hydromechanical transmission.

AAI Corporation’s proposal featured the same 75 mm gun in a cleft turret design and was to be powered by an Avco-Lycoming 650 gas turbine engine paired to an X-300-4A automatic transmission. Crew positions for both proposals were based on the HIMAG-B to varying degrees. AAI Corporation was awarded the contract in December 1977, with the construction of the vehicle being completed in 1979. Primary testing of the vehicle was completed in 1982, but the HSTV-L would continue to be used for firing and stabilization testing well into the mid-1980s. While ACVT testing was underway, AAI Corporation created a vehicle based on the HSTV-L called the RDF/LT (Rapid Deployment Force Light Tank).

This austere version of the HSTV-L was offered to the Marine Corps for the Mobile Protected Weapons System (MPWS) program, though it was never accepted. The Army’s counterpart to the MPWS program, the Mobile Protected Gun System (MPGS) program would eventually evolve into the Armored Gun System (AGS) program, from which the M8 AGS would eventually be developed.

Design

The HSTV-L was a remarkably small and light vehicle. The hull was roughly 19.38 feet (5.91 meters) in length, 9.15 feet (2.79 meters) in width, and the vehicle was 7.91 feet (2.41 meters) tall. With applique armor installed, the HSTV-L weighed 22 US tons (19.95 tonnes). The HSTV-L’s upper front plate was angled at 80 degrees. It was believed that this extreme angle, in conjunction with the HSTV-L’s special applique armor, would protect it from 115 mm rounds used by the Soviet T-62.

The driver and gunner were placed side-by-side in the hull, while the commander sat up in the turret. All crewmembers were in supine positions. The driver and gunner were both capable of driving and shooting, while the commander could only shoot. The gunner was provided with two sights. One was located on the right-hand side of the turret roof, while the other was located in the center of the hull. The turret-mounted sight possessed FLIR (Forward Looking InfraRed) imaging and a CO2 laser rangefinder. The commander was also equipped with a thermal sight, which was placed in the center of the turret roof. Both sights were stabilized and had two field-of-view settings. Outputs for the sights were displayed on CRT screens located in each crew position.

The HSTV-L’s gas turbine engine produced 650 gross and 600 net horsepower respectively. The engine, derived from one used on Army helicopters, was chosen for the HSTV-L due to its greater acceleration compared to diesel engines. The X-300-4A transmission had four forward gears and two reverse gears. The HSTV-L had a power-to-weight ratio of 29.5 hp/US ton (32.6 hp/tonne). Top speed on level road was roughly 52 mph (83.7 km/h).

Based on tests at the Waterways Experimentation Station in Vicksburg Mississippi, off-road speed was modeled and predicted in two primary locations; West Germany and Jordan. In Jordan, top speed was expected to approach 50 mph (~80 km/h). In Germany, the HSTV-L was expected to approach 35 mph (~56 km/h). This was quite fast compared to MBTs of that generation, with M60s and M1s only reaching 13 and 30 mph (21 and 48 km/h) in similar terrain respectively.

The HSTV-L’s non-adjustable hydropneumatic suspension system was provided by Teledyne. The tracks were derived from the ones on the M551 Sheridan. The vehicle sat on five doubled road wheels on each side, with the drive sprocket at the rear and the idler at the front. The track return was supported by three return rollers. The upper part of the track was covered by a side skirt meant to increase protection and reduce the amount of dust kicked up when moving.

The cleft-type turret design, wherein the gun is mounted in a space created in the middle of the turret roof, allowed the 75 mm XM274 cannon to have excellent elevation and depression angles, the former of which was important for its design goal of self-employed air defense. The main gun could theoretically depress to a maximum of 30 degrees and elevate to a maximum of 45 degrees.

The fire control system was quite advanced. It featured a rate-aided auto-track mode that used FLIR imaging to track both armored and airborne targets. The CO2 laser rangefinder was one of the first of its type and was chosen due to its ability to maintain relatively accurate range estimation through fog or smoke.

The Gun

The HSTV-L’s most particular component was the automatic 75 mm XM274 cannon designed by Eugene Stoner of Ares Incorporated. The L/72 cannon was originally designed with a sliding breech, though this was deemed too unreliable despite its impressive 120 rpm fire rate. The cannon was then revised with a revolving breech mechanism, wherein the breech would rotate out of line with the barrel in order to accept a new round. The ammunition developed for the gun was cased telescoped, meaning that the projectile was almost fully embedded into the propellant. This allowed for a novel autoloading approach wherein spent casings would be forced out of the breech by the new round. This approach was both fast and reliable. The HIMAG and HSTV-L took different approaches to feeder designs for the autoloader.

On the HIMAG, the six-round carousel that fed the breech was part of the gun cradle, meaning that the carousel would move with the gun as it elevated or depressed. On the HSTV-L, the six-round carousel was mounted directly below the gun breach in a static position. The breech would always remain in the same position relative to the turret, since it was mounted along the trunnion line. This allowed for both the carousel and gun to be replenished continuously despite the gun’s position. The HSTV-L’s autoloading system had immediate access to all 26 rounds carried. The carousel was replenished by a mechanized ammunition rack mounted in the right side of the turret.

On the RDF/LT, total ammunition capacity was increased to 60 rounds. The HSTV-L originally took 1.5 seconds to reload the gun, though this was decreased to roughly 0.85 seconds after the gun design was finalized. The gun could fire two rounds per second on a test bench, but the fire rate when mounted in a vehicle was decreased due to limitations with the stabilization and fire control equipment. The finalized XM274 design used the HSTV-L’s autoloader design over the HIMAG’s, as the HSTV-L’s design allowed for a wider variety of feeder designs. The XM274 cannon system consisted of the gun, the XM21 rammer, and an electronic control unit. This allowed the system to be mounted in a number of vehicles with differing feeder designs while keeping the reload rate constant. The system had dual-feed capability. When engaging targets the gun would ideally be fired in two to three-round bursts. This was done to increase the probability of a lethal hit.

The gun fired a variety of ammunition, including armor-piercing fin-stabilized discarding sabot (APFSDS), high explosive (HE), high explosive proximity (HE-P), and anti-aircraft multi-flechette. The ammunition used fiberglass casings which were originally developed for use with the Army’s 60 mm automatic cannon. The APFSDS round, a depleted uranium long rod projectile, was initially noted to have performance on par with the 105 mm round M774 used on the M1 Abrams. This was deemed insufficient and led to an ammunition development initiative called Delta 3. The gun breech was lengthened by three inches as part of Delta 3, allowing for a longer case and boosting muzzle velocity from 4,800 fps (1,463 m/s) to 5,300 fps (1,615 m/s). The Delta 3 round was designated XM885.

Delta 3 was followed by another initiative called Delta 6. Delta 6 could penetrate roughly 16.9 inches (430 mm) of rolled homogenous steel armor, though this too was deemed insufficient. Two 90 mm guns were developed and tested by Ares to address this lack of potency, but the Army would ultimately select conventionally loaded 105 mm guns for future light vehicles.

Besides the main gun, two 7.62 mm M240 machine guns were also present. One was coaxial to the main gun and a second was placed on the commander’s cupola.

The Boneyard

The sole HSTV-L currently resides at the Anniston Army Depot in Alabama. It is severely dilapidated. The hydropneumatic suspension system has lost pressure, meaning that the vehicle now sags significantly. Hatches have been left open, allowing for CRT screens to become cracked. The gun barrel is almost entirely rusted.

Conclusion

Though the HSTV-L itself or its direct successor, the RDF-LT, never saw service, it did provide a treasure trove of valuable information through testing. This information would go on to influence more successful initiatives, such as the M8 AGS. Though performance of the 75 mm exceeded then-current 105 mm ammunition, the 105 mm gun had more growth potential. It also would have been incredibly expensive to replace 105 mm ammunition stockpiles with 75 mm ammunition. In light of these revelations, 105 mm M68 derivatives were chosen for future light vehicle programs.

Sources

Sheridan: A History of the American Light Tank – R.P. Hunnicutt
Department of Defense Appropriations for Fiscal Year 1978
Department of Defense Authorization for Appropriations for Fiscal Year 1979
Department of Defense Authorization for Appropriations for Fiscal Year 1981
Department of Defense Authorization for Appropriations for Fiscal Year 1984
Department of Defense Authorization for Appropriations for Fiscal Year 1985
The TARDEC Story, Sixty-five Years of Innovation 1946-2010 – Jean M. Dasch, David J. Gorish
ADB069140 Aerosolization Characteristics of Hard Impact Testing of Depleted Uranium Penetrators
ADA117927 Armored Combat Vehicle Technology (ACVT) Program Mobility/Agility Findings
Jane’s Armour and Artillery 1991-92 – Christopher F. Foss
DoD Financial Management Regulation Volume 15, Appendix B
ADA090417 High Performance Vehicles
Extended Area Protection & Survivability (EAPS) Gun and Ammunition Design Trade Study
ADA055966 Feasibility Study of Filament Wound Cartridge Cases
Jane’s AFV Systems 1988-89 – Christopher F. Foss
Jane’s Light Tanks and Armoured Cars – Christopher F. Foss
International Defense Review No.1 / 1979
Jane’s Armor and Artillery 1985-86 – Christopher F. Foss
Armor Magazine Volume 85 January-February 1976
Armor Magazine Volume 89 July-August 1981
Antitank: An Airmechanized Response to Armored Threats in the 90s – Richard E. Simpkin
Army Research, Development, & Acquisition Magazine January-February 1981
Jane’s Armoured Fighting Vehicle Systems 1988-89 – Christopher F. Foss
Interviewing an HSTV-L Engineer – Spookston
RU 9532 Sessions 4 and 5 – Smithsonian Institution Archives

United States of America (1951-1958)
Light Tank – Design Only

On 2nd April 1951, James Joseph Baldine (20/12/1910 to June 1974) of Hubbard, Ohio, USA, submitted a design for a one man tank and, like so many other one-man tank designs, Baldine’s had all the advantages of protecting a single soldier behind armor but also all the same disadvantages of a lack of fightability, observation, and vehicle control. He had, however, carefully considered the control aspect of the one-man tank and devised a foot-pedal control system which would allow the soldier inside to manage the steering and propulsion of the vehicle entirely with his feet allowing him to keep his hands free to operate a weapon. Baldine was no doubt influenced by current events, as the design was submitted at the time of the Korean War (1950-1953) but showed what can only be described as naive thinking in military terms, especially in a post-World War II era. Nonetheless, the design was a thorough one, producing probably the best of all of the one-man tanks and showing how many of the challenges for such a concept could be overcome.

Automotive

Baldine’s tank did not separate the engine from the operator (this is what Baldine called the sole crewman), but placed it directly behind him, with the control pedals for steering/braking at his feet. The engine is described only as a four-cylinder, air cooled aviation type motor behind which was a conventional fluid transmission connected to the final drive for the tracks and a power-take-off with a small propeller allowing the vehicle to be propelled in water. Exhaust gases were vented directly out of the top but, with no provision for a fan, the operator would quickly become very tired from the proximity of this hot engine (despite the presence of a bulkhead between the operator and the engine) inside such a small machine. Directly under the crotch region of the pad, under the operator, was the petrol tank for the engine. The tracks for Baldine’s tank are not specified but he describes them only as “an endless track” with suspension of a ‘shock absorbing’ type.

Armament

The only mention of armament from Baldine is of a single machine gun in the front. The artwork submitted for his patent application in 1951 seems to indicate a .50 calibre machine gun like the M2 Browning. Fitted within a simple ball-mount in the nose of the tank, it would actually have a potentially wide arc of fire. Ammunition for it was fed from a magazine secured to the side of the nose-wall. A secondary weapon, in the form of a forward firing rocket launcher sticking out of the front, was located to the left of the operator. Fed from a magazine at the rear, the purpose of the rocket launcher is unclear as to whether it was for smoke or anti-tank or other purposes. The exhaust gas from the rocket was directed down below the vehicle to prevent it from giving away the position of the tank and the operator was provided with a sight to try and aim it. No other armament or smoke launchers were provided for, although presumably any soldier inside would also have their personal weapon as well, such as a submachine gun or handgun.

Layout

The tank itself was somewhat more complex than many other one-man tank concepts and also a lot larger. Unlike others, where the operator lacks enough space to sit up, Baldine proposed a taller vehicle with a pronounced dome directly over the soldier. Provided with ventilation slots, this dome would provide air and comfort for the solder but was not used for observation. Instead, all observation was conducted through the single large bulletproof glass window located directly to the soldier’s front over the main armament. Access to the tank was gained via a small sliding hatch located midway down its length on the roof, meaning the soldier would be exposed to enemy fire if/when the machine became stuck. 

The Pad

A common flaw in the one-man tank concept is the issue of comfort for the soldier crewing the vehicle. The operator is already very busy having to command, steer, and fight from the tank and obviously this is made harder if they are uncomfortable. Taking a prone position, where the soldier is lying on his front, can become very tiring after a while, particularly after travelling over rough country and having to lift their head up in order to see and fight, which produces additional strains. Baldine’s additional idea to assist his one-man tank concept was the addition of a specially designed sponge-rubber pad on which the soldier could lay. 

Specially shaped, this pad would hold the operator in a steady position, providing support for his arms and chin as well as a wedge shaped block on which his crotch would rest. This crotch-block would prevent the solder from slipping down the mattress and raised edges on the sides and base would stop him from sliding laterally as well. 

Conclusion

The one-man tank idea, something first proposed decades earlier and something which had never seen any successful mass production or use, was a dead idea by the 50’s. It can be surmised that Baldine was motivated by seeing the War in Korea and wanting to do his part for his country and to save the lives of soldiers or maybe just opportunism to try and make some money from an idea. Regardless of his motivations though, the design itself was not a terrible one by any means. As far as the concept goes, the design certainly had merit for the control of the machine and the layout, but the concept of a one-man tank was just fundamentally a bad one. A single soldier would be unable to adequately command, control and fight from the vehicle and the features of the vehicle inherent within the design, such as the low profile, giving low visibility, prevent such an idea being viable. As such, his one-man tank design might have been a very good one-man tank design but the concept was simply a flawed one. As such, his design suffered from those flaws and despite his best efforts could not overcome them. That ended his one-man tank idea.

Baldine also submitted a patent for a game teaching apparatus in January 1951. In 1963, he also designed a portable incinerator for a motor vehicle, designed as a means of disposing of cigarettes and paper items which could be fitted to a standard saloon car for disposing of litter on the move. Neither of those two designs were perhaps as adventurous as his one man tank idea, but Baldine had moved on anyway. It is not known whether Baldine received any financial benefit from his patents, but his one-man tank idea certainly went nowhere. His political career, as Mayor of Hubbard, was far more successful though, serving six consecutive terms. He died in office in 1974.

Sources

US Patent US2823393(A) Cushion pad for one-man tank, filed 2nd April 1951, granted 18th February 1958

US Patent US2722986 Braking and Steering Control Mechanism for one-man tank, filed 2nd April 1951, granted 8th November 1955

Hubbard News, 19th June 1974 – Mayor Baldine: an era has ended