Based on the Carden-Loyd Mk.VILike the Vickers 6-ton and the Vickers Amphibious model acquired at the same time, the Soviet Union’s UMM special commission bought the Mk.VI in 1929, already a world market success. This was the export model, characterized by a rear engine compartment and a pyramidal structure protecting the crew’s heads. It corresponded to an Army requirement for a light reconnaissance tank. The vehicle undergone a series of trials but production was delayed as the general staff was displeased with it. A preseries was apparently built (unknown quantity) on the original British plans in 1930. Changes were made by Chief Engineer N. Kozyrev and chief Engineer K. Sirken at Zavod No. 37 near Moscow in 1931. They included a scaled-up hull, many reworked details to cope with the Russian climate and terrain, new engine and transmission, a new, sturdier running gear, extended rear storage and a new mount for the main machine-gun, the Soviet-built 7.62 mm (0.3 in) DT, fed with 2520 cartridges.