Major Philip Johnson, the unofficial head of Central Tank Corps Workshops in France, as soon as he received them began fitting one of the Whippets with leaf springs. Later, in 1918, he fitted this vehicle with sprung track rollers, Walter Gordon Wilson's epicyclical transmission from the Mark V and a V12 Rolls-Royce Eagle aero-engine. A top speed of about was reached. This project made Johnson the best qualified man to develop the later fast Medium Mark D, which looks like a reversed Medium A. Other experiments included the fitting of a large trailing wheel taken from an old Mark I tank and attaching a climbing tail, in both cases attempts to increase trench-crossing ability.