Steam Wheel Tank

The Steam Wheel Tank was the official US Army name for the vehicle also known as the three-wheeled steam tank. It was an early U.S. produced tank built by the Holt Manufacturing Company (now Caterpillar Inc.) sometime between late 1916 and early 1917. It was the third tank to be designed in the U.S. and was completed in 1918.

Design
The Steam Wheel Tank was designed on the basis of the early "Big Wheel" Landship concepts put forward by Sir William John Kelly from Great Britain in 1915 and also resembles the German Treffas Wagen of 1917.

Construction
It had two large eight feet diameter wheels with three feet wide treads, located at the front on each side of the substructure. These wheels were made out of several sheets of pressed steel and were not specially manufactured, being of the type used on Holt agricultural machinery of the period. At the rear was a four foot diameter roller wheel to be used for steering. A small skid plate or tail was attached to this roller to assist in trench-crossing. Both front wheels were driven by individual power units which consisted of a Doble 2 cylinder 75 hp steam engine and Doble kerosene fired boiler.

Armaments
The vehicle's main armament was a 2.95" (75 mm) mountain howitzer mounted low in the front. A .30 caliber Browning machine gun was carried in a ball mount on each hull side. Its riveted armour plating was between six and fifteen millimetres thick.

Prototype
One prototype was completed in February 1918 and was evaluated between March and May 1918 at Aberdeen Proving Ground. Some reports of the evaluation state the tank became stuck after fifty feet, thus ending its evaluation.