The first real field test of the design was carried out in August–September 1943, when examples of the Centaur, Cromwell, Sherman M4A2 (diesel engine) and Sherman M4A4 (multi-bank petrol engine) were tested in Exercise Dracula, a long trip around Britain. The Shermans proved to be the most reliable by far, requiring 420 hours of specialist fitter attention over a total distance travelled of . This corresponds to 0.03 hours per mile. In comparison, the Cromwells drove and required 814 hours, or 0.07 hours per mile. The Centaur managed only due to constant breakdown, and required 742 hours, or 0.087 hours per mile.