I'm not sure why military people thought the future was 3 wheelers but to rival the Moto Guzzi oddity, here is the entry from Straussler.
Nicholas Straussler was a Hungarian-born automotive engineer working in England, becoming a citizen. He was known for a series of innovative trucks and tractors in the mid thirties, and one of the designers of the floating DD tank system. Postwar he came up with what he called Lypsoid tires, fat low pressure tires which he thought could replace tank tracks as well as provide better floatation for conventional wheeled vehicles. One of the test vehicles was this 2 stroke twin powered thing, basically the forerunner of the ATV!
Below, Lantrac from 1969, about the time the Honda ATC was introduced.