This was a British undertaking to evaluate the relative reliability of the British Centaur and Cromwell cruiser tanks and the US M4 Sherman medium tank (August 1943).
The Cruiser Tank Mk VIII Centaur (A27L) was a version of the Cromwell tank powered by a Liberty engine. It was not in itself a great success, and many Centaur vehicles were converted into or completed as Cromwell tanks, and in that configuration were used in combat in North-West Europe.
The Centaur was really a tank which should never have been built. Late in 1940 W. A. Robotham, a senior Rolls Royce designer, led a team that converted the Rolls-Royce Merlin aero engine into the Meteor tank engine. This work was triggered by a October 1940 meeting between Robotham and Henry Spurrier, the general manager of Leyland Motors. Spurrier was worried about the low power of the Liberty engine being used in new British tank designs. At first Leyland agreed to produce the Meteor, but then backed out and decided to continue building the Liberty.
At this point the Ministry of Supply should have stepped in to force Leyland to build the much more powerful Meteor, but instead and perhaps inevitably compromised. English Electric and the Birmingham Carriage & Wagon Company were to produce the Meteor-powered A27M Cromwell III while Leyland was to produce the Liberty-powered A27L, then known as the Cromwell II. The design of the A27 would first be modified to allow it to take either engine.
It is unclear how many Centaur vehicles were later re-engined, but a significant number of tanks were built from scratch with Centaur hulls and Meteor engines and designated as Cromwell tanks.
The first A27 was competed in July 1942, and the name Centaur was adopted in November 1942. Tests showed that the overworked Liberty engine had an even shorter life and was less reliable in the Centaur than it had been in the preceding Crusader.
In August 1943 the Centaur and Cromwell were pitted against the Sherman M4A2 and M4A4 in the ‘Dracula’ (i) reliability test, which was a 2,300-mile (3700-km) trip round various armoured units. The Sherman performed best, the Cromwell was next and the Centaur was a poor last, often arriving at the night’s halt hours after the other tanks.
After several months of further modifications the Cromwell and Centaur were put through another hard test in November 1943. This time the Cromwell proved reliable, but the Centaur still struggled, and it was fully clear that the basic problem was that the Liberty engine was not powerful enough for the weight of the tank, and that its poor power/weight ratio meant that the engine had to be overworked and therefore tended to fail. Despite this failure, large-scale production continued, with eight different industrial groups committed to production of the Centaur.