Tank History - Inter-War Tank Development
In 1932, there was a track development that went unnoticed at the time but has revolutionized tank-track performance ever since. This was the rubber-bushed track. Since the first tanks were built, they had used “dry pin” tracks, invented for use on tractors of the “caterpillar” type. Dry-pin track had a very short life – never more than 500 miles – because dirt got into the track-pin bushings and wore the pins out. The T1 rubber-bushed track, developed in 1932 by the Army and the Timken Bearing Company, used flexible rubber bushings to replace dry track pins. Even the first rubber-bushed tracks ran 1,000 or more miles. They are still a basic element in U.S. Army tank-track design.
The second tank innovation introduced in 1932 was the volute-spring suspension. This is a bar coiled on edge like a clock spring. One end is the inner coil, the other the outer. Its big advantage is that it is very rugged and the most powerful compact spring there is, so it took up the least possible space in a tank suspension system – a fraction of what a leaf, coil or torsion-bar spring requires.
While the new components were undergoing test and development, the Army was also pursuing Christie’s designs. The Army decided to pursue several other lines of development besides Christie’s because of these problems. This turned out to be a very farsighted decision in light of the problems both the British and Russians experienced with their Christies in World War II.
At about this time, Gladeon M. Barnes, later an Ordnance Department major general, patented the torsion-bar suspension. The torsion-bar suspension takes up room in the bottom of the tank hull instead of along its side.Shortly after this project was underway, Rock Island Arsenal built a T4 Medium, a 13-tonner, which was supposed to be the T4 Combat Car but weighed more than regulations allowed for a combat car. The T4 Medium was later rebuilt as the T4E1 to try out a special casemate top hull, but neither T4E1 nor the T3E4 Medium Christie were considered very successful.
In 1934, Rock Island Arsenal built the T2 Light, a turreted design with a 37mm gun, rear engine and front drive. It weighted 6.5 tons, and its 120-horsepower engine gave it a speed of about 25 mph. It used a version of the Vickers-Armstrong six-ton tank’s suspension. It was a reasonably good vehicle but not nearly as good as another design built at the same time.
Two experimental tanks built at Rock Island Arsenal in 1934 had a tremendous influence on the development of U.S. Army tanks used in World War II. One was the T2E1 Light Tank, the other the practically identical T5 Combat Car. These machines combined for the first time the rear-mounted, air-cooled, radial aircraft engine with a front drive, a volute-spring suspension and a rubber-bushed, long-life track. They were a fantastic success. They could do 45 mph, which made the convertibility of the Christie design unnecessary. They had excellent mobility. Track life proved to be more than 1,500 miles, and the tank did not throw tracks during violent maneuvering. Their overall performance was unheard of in any other tanks of their day.
In 1936, an improved twin-turret model of the T2E1 Light was standardized and put in production at Rock Island Arsenal as the M2 Light Tank. Along with it, a single-turret version was standardized and went in production as the M1 Combat Car. These tanks were identical except for turret arrangements, and they were the first in the highly successful World War II light-tank series. Until the M2 Light Tank and M1 Combat Car were standardized, the only standard tanks still listed in the Army’s inventory were World War I types: the six-ton Model 1917 of the French Renault design and the 40-ton Mark VIII of the British type. The Army was still using them, along with some of the earlier Army experimentals, to train and educate tank troops.
Another experimental tank, built at Rock Island Arsenal in 1934, shared the same new design features. Called the T3 Light, it was a turretless three-ton machine that worked well, but it was never pursued because the Army had no requirement for it.
The Army, having a standardized light tank and combat car, needed a medium tank. In 1937, Rock Island Arsenal designed and produced the T5 Phase I Medium. Its power train was derived from the M2 Light and M1 Combat Car, with a rear engine, front drive, volute suspension and rubber-bushed track. In addition to a 37mm gun in the turret, there were four corner casemates mounting .30-caliber machineguns. It had a 350-horsepower radial air-cooled aircraft engine, and it could do more than 26 mph. Its suspension and track parts were the same as those on the new light tank and combat car. It was a success.
Later variants of the medium tank project included the T5 Phase II and T5 Phase III of 1938, the latter employing a wider, improved volute suspension and rubber-bushed track. In 1939, this design was standardized and put in production as the M2 Medium.
In 1939, a production M2 Medium was used to test the Guiberson radial, air-cooled diesel engine as a power plant. This was called the T5E1. By 1939, Rock Island Arsenal was producing the M2 Medium and working on the T2E2 Medium. The T2E2 used the lower hull and power train of the M2; it had a unique new top hull with a machinegun turret on top, a 75mm pack howitzer in the right front corner, and machine casemates on the rear corners. It was never intended to be anything but an experimental machine to test large-caliber cannon in the hull, and it proved to work well enough.
The rubber-bushed track, introduced in 1932, is still in use. As far back as World War II, sets ran as far as 5,000 miles before replacement, and there is still nothing better.
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