The T-40 was an amphibious light tank used by the Soviet Union. It was intended to replace the aging T-37 and T-38 tank light amphibians. It was a superior design, but due to the pressures of war the Soviets favored the production of simpler tank designs, and only a small number of T-40s were built.
In FHSW the T-40 is able to cross rivers and lakes without problem, this can be used to scout enemy positions that are hard to reach usually. It’s also possible to spot targets for the artillery while sitting savely in the tank. The armor is only about 13 mm thick so don’t expect to survive tank battles.
The Russians tried to improve the weak combat value of the T-40 by developing an improved variant with better armament. They modified the hull and redesigned a 23 mm AA gun to fit it in the tank. A prototype was built and tested in 1941 but the cannon didn’t work properly which led to the dismissal of the project.
In FHSW the cannon of this improved T-40 is comparable with the German 2 cm Flak 38 which is enough firepower to penetrate the sides of the Panzer III and IV.