At the same time as negotiations with the US, problems were being encountered with the use of the Vickers 75 mm HV gun in the Cromwell, with a larger turret ring being required. This was now expected to be introduced in mid 1944, leaving the majority of Cromwells with the medium velocity gun similar to the Sherman. Design of the high velocity variant was split to a separate specification. Intended as just another version of Cromwell, the new A34 version eventually needed significant re-engineering leading to production of the A34 Comet, which used a high velocity gun firing 17-pounder ammunition from a gun by a smaller cartridge down a shorter barrel. In the interim, the A27M version started.