The Russians admired the robust and simple automotive design of the 1940 British Mk III Valentine, but were merely polite about the tank's main armament, which fell well below Eastern Front requirements. Some tanks had their main armament replaced by 76.2mm (3in) guns in factories in the USSR. The narrow tracks were also reported to be a problem in winter, first clogging with snow, then freezing, and immobilizing the vehicle.
Designed by Vickers-Armstrong in 1938, the Valentine was a private venture project drawing on their experience with the A9 and A10 Cruiser designs. Rather quaintly, the Valentine took its name from the fact that its plans were submitted to the War Office close to the date of St Valentine's Day in February. The War Office took over a year to make up its mind, since there were some reservations about the two-man turret, which was thought to be too small to be upgunned. However, when they committed to the project, they requested that Vickers-Armstrong make the first delivery in the shortest time possible.
Production ceased in 1944 after a total of 8275 tanks had been built by three companies, representing a quarter of British tank output. There had been plans to stop production in 1943 on grounds of obsolescence, but it had continued for the extra year to satisfy Soviet requirements. The Valentine was produced in Britain by Metropolitan-Cammell and Birmingham Carriage & Wagon, as well as Vickers, and in Canada by Canadian Pacific of Montreal; here, of the 1420 Mk VI tanks produced, all but the 30 retained for training went to the Soviet Army.
The Valentine was originally armed with a 2pdr (40mm (1.57in)) gun, but this was upgraded to a 6pdr (57mm (2.24in)) gun in the Mark VIII, IX and X. The Mark XI, fitted with a 75mm (2.95in) gun, was the final production type. Reliability and performance was improved when a GMC two-stroke diesel was installed, replacing the AEC petrol or diesel engines. Production speeded up when all-welded construction replaced all-riveted.