Designed by Nikolai Dyrenkov in 1931-1932, the D-6armored railcar was powered by a 95hp Hercules engine. It was envisaged as a single-turret 107mm gun carrier. Instead, the car was completed with 76mm guns in two turrets, similar to serial-produced D-2 (another Dyrenkov design) but with different engine/transmission layout. After successful tests in 1933, the D-6 was sent to the Far East. Only one built.