Tuesday, April 14, 2015

Swinton and Holt

One unusual American prototype of the tank was the gas-electric hybrid built by Holt. It had a crew of six and used a Holt four-cylinder motor to turn a generator in order to power two electric track motors. This design was later used for giant mining trucks and highway construction vehicles.

General Swinton visited Benjamin Holt in Stockton, California, to salute him for his contribution to the war effort and to inspect the Holt one-man tank prototype. Because the war ended, the tank was never manufactured.

Most tanks used in World War I were of European manufacture, but the Caterpillar and Bullock tractors had much influence on some designs. In France there were differences and conflicts in the approach to tank design. As an example, the French Schneider Company bought two 45 hp Baby Holts (Holt 75) in April of 1915 and used these as a basis for their versions, which had one 75 mm gun and two Hotchkiss machine guns. The whole tank weighed 13.5 tons. It was first tested at the Aberdeen Proving Ground in Maryland.

General Ernest Swinton traveled to Stockton in 1918 to meet with Benjamin Holt to express his gratitude for the company’s contribution to the war effort. Holt had also built a gun-mount Caterpillar tractor capable of carrying a 75 mm gun at the then unheard-of speed of 28 mph. Advances in metallurgy made this a possibility so that transmission components would not disintegrate from heat and friction, but it would be a number of years before this would be proven in the field. A one-man tank prototype was also developed by Holt/Caterpillar in Stockton, but it never went into production. Existing photos show General Swinton thanking and shaking hands with Benjamin Holt surrounded by Stockton factory workers in front of a wooden mock-up of the tiny one-man tank.

Another single prototype was built by Holt in conjunction with General Electric Company (GEC). It was completed in January of 1918. It used lengthened and upgraded iterations of the Holt tractor with pivoting track frames on vertical coil springs and ten road wheels on each side. The Holt Gas-Electric used a 90 hp Holt four-cylinder motor to drive a GEC generator that powered two electric motors, one for each track. By varying the current in addition to the brakes on each shaft, the tank could be steered more easily. This vehicle had a 75 mm gun in the nose and a .30-caliber Browning machine gun on each sponson. The engine and transmission at the rear nearly blocked the only door in and out of the tank with a crew of six: commander, driver, gunner, loader and two machine gunners. Only a prototype was built, but with its weight of 25 tons it had considerable shortcomings in climbing and speed, which was about 6 mph at best. Armor was between 1.4-inch and 3.4-inch thick depending on section area.

This design was later used by a few companies, such as Caterpillar, to build huge roadbuilding trucks and graders, even up to this day. There was also a 20-ton tractor mounted with a truck body, and this crawler was used to build yet another prototype also called the ‘American Tank.’

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