The Guy 6×6 vehicle was only on loan for testing prior to being sent out to India and arrived at MWEE in March 1931 for a demonstration to compare its performance against that of an experimental 8×8 Guy vehicle delivered the previous year. The 8×8 vehicle was itself a development of the standard Guy 6×4 chassis used for the Indian Army armoured car and ammunition lorry. The Guy 8×8 vehicle was intended to be used as a salvage or heavy haulage vehicle with greater tractive effort and better cross-country performance , without any appreciable increase in size and without departing too much from standard design. The vehicle was fitted with a 95hp six-cylinder engine and a supplementary gearbox to provide power to the two front axles and the winch.
Comparative trials with the 6X6 vehicle were held in February 1931 at MWEE and in North Wales. The general conclusions reached were that the added expense and technical complications of the 8×8 were not justified by any great gain in performance except in exceptional circumstances. The bevel gear pinions of the front-wheel drive gave constant problems throughout the trials and experiments were finally brought to a halt in 1933. The conclusion at the end of the trials was that the 8×8 vehicle achieved an overall gain in tractive effort in the order of 10 per cent but at the expense of increased fuel consumption, greater weight, increased cost and difficulty in maintaining the complicated transmission system.
Just before the Guy 6×6 was shipped out to India in March 1931, a demonstration was held to compare its performance against the 8×8 hauling the 3in 20cwt AA gun. At the trial it was generally considered that the performance of the 8×8 was better, despite the fact that it was some two tons heavier. The Guy 6 x 6 was never adopted for AA gun haulage in the British Army. In India, it took part in comparative trials against the 6×4 Guy and Thornycroft vehicles and the Holt 5-ton tractor as a medium artillery tractor but was not adopted in that role either.