The vehicle served mainly in Operation Barbarossa and the defense of Moscow, and it was rarely seen after that point, although it was used in Soviet training schools until 1946.

[7][8] The welded, conical turret shape improved protection, although the armor was still very thin.

[11][12] The T-40 entered production just prior to the outbreak of war, and was intended to equip reconnaissance units.

As the need for large numbers of tanks became critical, a secondary non-amphibious variant was designed on the T-40 chassis.

Due to delays with design of newer model, T-40 was modified to have thicker armor, 20 mm TNSh autocannon, simpler spoken wheels and absent water propulsion system.

[13][14][15][16] A small batch of "T-40" T-60 were produced with BM-8-24 Katyusha rocket racks mounted instead of a turret.

The type was very rarely seen after the end of 1941, although some T-40s remained in service as late 1946 in some school units.