Foster-Daimler tractor

The December 1914 acceptance trials included a bridging demonstration where a tractor towed two trailers of bridging timbers to a broad ditch; after engineers spanned the ditch, the tractor and trailers were waved across and one of the trailers toppled over the side, collapsing the bridge.[2] After this accident Bacon remarked to Tritton that an armed and armoured vehicle that could lay its own bridge would be of great value.[2] Bacon continued to press Tritton about the idea and designs were drawn up for a modified Foster-Daimler tractor capable crossing a gap. These were presented to Winston Churchill by the end of December and an order was placed for the production of an experimental prototype.[2]

The prototype, known by various names including the Tritton trenching machine, the Tritton trencher and the Tritton trench crossing machine, consisted of a Foster-Daimler tractor with the usual front wheels removed and a sub-frame fitted to the front of the chassis which had two wide road wheels in tandem – increasing the vehicles overall length to approximately 31 ft (9.4 m) – and two steel bridging girders 15 ft (4.6 m) in length were hung below the chassis on either side.[2][4][3] As the vehicle approached a trench the front wheel would protrude across, and as it made contact the girders were lowered allowing the machine to drive across the trench. Once across, the vehicle would winch the girders across, reverse over them and be prepared to cross another trench.[2][4][3] Bacon proposed fitting every trencher with a pair of headlights and another light on each side of the vehicles, each with glass 2 feet (0.61 m) in diameter and painted with the head of a ferocious Chinese warrior to unnerve the enemy during night attacks.[2]

Initially, the machine was to be ready for demonstration by 1 February 1915. This was subsequently delayed to mid-February but due to further various delays did not occur until 9 June 1915.[2] The machine had little difficulty in laying the girders over single trenches 8 ft (2.4 m) wide, but after crossing it required at least 25 ft (7.6 m) of clear ground to retrieve the girders. It was also found to be extremely nose-heavy, too cumbersome, and underpowered.[2][3] Despite the design's ingenuity, it was found to be impractical and the tractor was returned to its original configuration at a cost of £20.[2][3]

Probably the greatest contribution the Foster-Daimler tractor made to the war effort was to bring William Foster & Co, and particularly William Tritton, into the development and production of the tank.[1] Tritton was one of the engineers who developed the first completed tank design, Little Willie and its successor "Mother" ("Big Willie"), as well as the Mark A "Whippet" and Mark C "Hornet" medium tanks, with William Foster & Co. conducting much of the production.[1][5]

Little Willie, Mother, and the unchanged Mark I tank used the Foster-Daimler tractor's 105 brake horsepower Daimler engine, gear-box and differential, as it was one of the few power units available in England with the required power, speeding up development and production.[4][3][6] They were also used in the Mark II, Mark III, and Mark IV tanks. Later, to increase the power of the engine, it was modified with aluminium pistons and dual carburettors to deliver 125 brake horsepower (93 kW), the upgraded engine being installed in the last 200 Mark IV tanks.[3][6]