Tim Gosling explains the 1912 Subvention scheme
In 1900 the British War Office formed the Mechanical Transport Committee to consider the use and purchase of steam and internal combustion engine transport as a replacement for horse transport.
A series of trials were arranged where manufacturers would compete against one another in a range of tests to win a cash prize. The first trials were won by steam wagons while those powered by internal combustion engines demonstrated a distinct lack of reliability.
With improvements in design the capability of the internal combustion engine was demonstrated in 1908 when 500 troops were quickly transported in 24 London omnibuses from London to Shoeburyness and again in 1909 when a complete Battalion of Guardsmen was transported to Hastings in 286 cars and 30 trucks.