The T92 Light Tank - Canceled Too Early - Tank Historia

The T92 Light Tank – Canceled Too Early

The T92 dates back to the beginning of the Cold War, when the US military was busy updating its arsenal of Second World War-era weapons to more modern-day equipment. With the Korean war now in the rear-view mirror by the mid-1950s, the US Army finally had some breathing room to sit down and take a long, hard look at some of its more antiquated weapon systems, particularly light tanks.

The M41 Walker Bulldog was one of the US’ first post Second World War light tanks, intended to replace the M24 Chaffee. Unfortunately its development was accelerated by the Korean war, and the resulting tank was not as light and small as the Army had hoped

Such sentiments forced the US to continue its search for a proper light tank.

M41 light tank Georgia.
At 26 tons the M41 was nearer to WWII-era medium tanks than a light tank. Image by Georgia National Guard.

Army leadership turned to the US defense industry to propose a vehicle that had the firepower and armor protection of the M41, but a lighter weight and with a much smaller silhouette. Several companies put forward designs, all competing for this lucrative government contract.

Eventually, the most innovative design by Aircraft Armaments Incorporated, known as AAI, won out. The Army hoped that its unique design features would propel American light tank technology well past anything the Soviets could produce.

However, startling information about a potentially better Soviet light tank eventually forced Army leadership to abandon the project due to outside political pressure.

Contents

Background

Because the Korean war had forced the acceleration of the M41 Walker Bulldog program, the Army knew that it did not fully meet their needs. Even before the first M41s became operational in 1953, the US Army Ordnance Committee approached the defense industry with an inquiry into the M41’s replacement.

The Army stipulated that the tank could weigh no more than 20 tons, with a preferential weight of about 18 tons, and must sport the same 76mm gun as the M41. Over the next year, numerous companies worked on design concepts, but by July 1953, the Army chose the top three contenders for the project.

The first one was the Detroit Arsenal. Its design was rather unassuming, with the exception of an oscillating turret. The Detroit design did have the advantage of having the largest ammunition capacity of the three with 76 rounds on board.

Detroit T71 mockup.
This scale model depicts Detroit’s proposed light tank.

However, for unknown reasons, the Army scrapped this design and told General Motors and AAI to continue developing their proposals into full-scale models.

While General Motors had a rather simple design – essentially a reduced version of the M41 with a conventional turret – the AAI design was quite unique. All three designs had similar armor and firepower, but the most exciting feature of the AAI proposal was its cleft turret.

A cleft turret is a tank turret with the gun situated between one or more armored cupolas. For the AAI design, the team put an armored cupola on either side of the main gun. The tank commander sat on the right while the gunner sat on the left.

The front of the T92's odd turret.
Front view of the T92, showing its unique cleft turret. Note the two cupolas on either side of the gun. Image by Mark Pellegrini CC BY-SA 2.5.

Once the Army nixed the Detroit proposal, they designated General Motors and AAI’s proposals’ as the T71 and T92, respectively. After about three years of work, in January 1956, Army leadership told General Motors that they were cancelling their project.

Why did the T92 survive, and not the T71? Well, this was mainly a result of a lack of funding and the fact that by this time, the T92 was much further along in development than the T71.

The T92’s Unique Design

The first prototype AAI built fit the Army bill perfectly. Weighing in at 18 tons, the vehicle was at the upper threshold of what the military needed. The design shaved off almost 8 tons of weight compared to the M41.

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Weight was reduced by strategically replacing steel components with lighter metals and alloys. For example, the internal doors linking the different compartments inside the tank were made of aluminum, and the fenders were a mixture of aluminum alloys and fiberglass.

It had a maximum armor thickness of 32 mm, and made use of intelligently laid out armor to match the M41’s level of protection.

Light tank lacking rear idler.
The T92. The driver’s periscopes can be seen below the turret on the right. An eight cylinder engine is located below the grille on the left.

The compact design of the T92 was also much smaller than its M41 counterpart, helping to keep its weight down. Coming in at 2.2 meters (7 ft 5 in) tall, the T92 was about half a meter a shorter. It was about the same width as the M41, coming in at 3.1 meters (10 ft 4 in), but it was significantly shorter.

The T92 was just 6.3 meters (20 ft 7 in) in length, compared to the M41’s length of 8 meters (26 ft 6 in).

Its primary armament was the T185E1 76mm gun, which was essentially the same weapon used by the M41.

T92 and M41 back to back.
This image gives a good idea of the size difference between the T92 and M41 tanks.

Depending on the ammunition the T185E1 had excellent anti-armor capabilities. The M319 high velocity armor-piercing rounds could penetrate over 200 mm of vertical armor at around 900 meters. To put this into perspective, these numbers are similar to the 8.8 cm PaK 43, which was one of the deadliest anti-tank guns of the previous decade.

Back then tanks weighing 50-70 tons carried this sort of firepower, but in the 1950s this power could now be found on tanks weighing less than 20 tons.

However, there was a significant difference in that the T92’s gun was semi-automatic. Instead of physically ramming the round into the breech, the loader could place the round into a cradle that forced it inside.

M41 light tank 76 mm gun.
The T185E1 76 mm gun used in the T92 was essentially the same as the armament on the M41. Some changes had to be made to adapt it to the T92. Image by peettriple CC BY-SA 3.0 de.

This system reduced the physical toll on the loader, who could begin picking up the next round before firing the last one. As a result, the overall fire rate was an impressive 12 rounds per minute.

The gun also automatically dispensed spent casings outside the tank. Doing so was more of a practical requirement than anything else simply because space inside was so limited. This small tank contained a crew of four, (commander, gunner, loader, and driver) along with 60 rounds of ammunition and thousands of rounds for its .50 caliber and .30 caliber machine guns.

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The armored cupolas on either side of the 76 mm gun contained a .50 caliber machine gun for the commander and a .30 caliber for the gunner. Each cupola had a field of fire of 194 degrees and could traverse inward by ten degrees forward and four degrees backward. The turret itself could move 360 degrees and had an elevation of between 20 and negative ten degrees.

T92 at Aberdeen Proving Ground.
The T92 had a remarkably large turret ring for its size at 2.26 meters (89 inches). This was even larger than the M48 Patton’s turret ring. Image by 270862 CC BY-ND 2.0.

Interestingly, the T92 featured a small double-door at the rear of the hull for ammunition loading, however this could also be used as access to the crew compartment.

This tiny titan was powered by the Continental AOI-628-1, a 10.3 liter (628 cu in) gasoline-fed 8 cylinder opposed engine located in the right right of the hull. Though it could produce 350 hp, it palled in comparison to the 14.6 liter (896 cu in), 500 hp engine in the M41.

Because of this, the T92 had a top road speed of just 35 mph compared to the M41’s 45 mph, despite its lower weight.

T92 light tank rear doors.
The rear of the T92, showing its split doors. Note the brackets on the lower corners of the hull rear. This was where an idler was fitted during testing. Image by 270862 CC BY-ND 2.0.

The T92 sported an innovative suspension system called torsilastic suspension. Though quite common today in all kinds of commercial trucking and civilian industries, torsilastic suspension was unique at the time.

In traditional suspension systems, torsion bars and metal springs help support the tank as it moves. In a torsilastic suspension system, these metal springs are replaced with rubber bushings. This system requires less maintenance and provides a quieter and smoother ride.

And, as an external system, it does not take up interior space, unlike Christie or torsion bar suspension.

The final surviving T92 light tank at Aberdeen Proving Ground.
The T92’s suspension was quite radical for the day. Image by 270862 CC BY-ND 2.0.

Testing and Service History

After the first and second test models of the T92 were delivered in November 1956 and July 1957, respectively, Army engineers at Aberdeen Proving Ground put the vehicles to the test. Though the vehicle performed well overall, many mechanical and design issues had to be addressed.

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One of the biggest issues was the new T110 tracks used on the vehicle. The T110 design consisted of 16-inch wide, cable-reinforced rubber tacks, but these had a habit of breaking on a regular basis during tests. The ineffective tracks on the first two models were replaced with slightly thinner T85E1 double-pin tracks from the M24 Chaffee.

The T92 also had a propensity to throw its tracks. The original design called for four road wheels on each side. However, to solve the track-throwing issue, the team implemented a compensating rear idler wheel to help maintain tension.

T92 light tank with upgrades after testing.
T92 with 14 inch wide T85E1 tracks and a rear idler.

While these were the two most significant changes, the testing team recommended or implemented more than 50 changes during the two years the T92 graced Aberdeen Proving Ground.

While the team continued to perfect this promising light tank, in January 1957 Congress had gotten word that a new Soviet tank had been developed with amphibious capabilities.

Not wanting to be left behind, Congress members pressured the Army to acquire a vehicle that could match or supersede what would eventually be known as the PT-76 amphibious tank.

The only thing the Army had that could potentially match the PT-76 was the T92. However, for it to have an amphibious capability the T92 would require an entire redesign of the hull, which was impossible to do this late in development.

A Soviet PT-76 amphibious light tank.
A Soviet PT-76. This vehicle spurred the development of the M551 Sheridan. Image by Iamthewalrus241167 CC BY-SA 4.0.

Since the existing T92s could not be modified to become amphibious, the Army ordered the cancellation of the project in 1958.

The cancelled T92 made way for one of the most well known, and controversial, US tanks of the Cold War, the M551 Sheridan.

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Fortunately one T92 survived the project’s cancelation, spending many years outside in the Army Ordnance Museum at Aberdeen Proving Ground. The T92 was relocated to Fort Lee, Virginia in 2010 when the collection was transferred.