T-26-4: artillery tank with enlarged turret armed with the 76.2 mm KT tank gun mod. 1927/32 (some modern sources mention this tank as T-26A, A stands for artilleriysky or "artillery"). The turret of the T-26-4 was quite similar to main turret of the T-28 medium tank.
The T-26-4 with the KT tank gun passed tests successfully and five vehicles were built in 1933–1934 as pilot batch. Initially it was planned to arm three of these T-26-4 with the 76.2 mm KT tank gun mod. 1927/32 and the other two tanks with the 76.2 mm PS-3 tank gun. All five experimental T-26-4 artillery tanks were tested during military exercises near Leningrad in September 1934 before scheduled series production of 50 such vehicles in 1935. But on September 19, 1934 an incident with a T-26-4 took place: a blow-back because of shell case destruction during gun fire. Despite the fact that this defect was unrelated to turret design, the military representatives cancelled the order to produce the T-26-4.