The Medium Tank M4E3 was an experimental version of the Sherman that was powered by a Chrysler A65 engine.
The A65 was a V-12 water cooled petrol engine that had been developed by Chrysler, that was expected to produce 650 gross HP or 575 net HP. In January 1943 the company asked for permission to install the A65 in an M4, and in March they were given an M4A4 for their tests. The modified tank was given the designation M4E3.
The A65 was a sizable engine, and even the long M4A4 had to be extended by another 9.5in to fit in it, giving the tank a sloped back. It was also quite a narrow engine, so there was plenty of space on either side of the engine. The M4E3 used the normal M4 power train.
The M4E3 was ready by the end of May 1943 and underwent comparative tests against a M4A4. In these tests the new engine performed well. Acceleration was particularly good, and outperformed the M4A3, which used the Army's preferred Ford engine. After 400 miles the test engine was removed for checks, and was found to be in good condition.
Despite this impressive performance, the A65 powered Sherman wasn't put into production, and the research programme was ended on 22 November 1943.