In August 1939, 6 chassis were given to the Inspectorate for Engineers to use for bridge laying tanks. Changes were an altered motor mount, improved turret race, redesigned gun mantlet housing, and an armored sleeve to protect the coaxial MG. Starting at chassis no. 80341 the engine was modified to improve carburation. Starting in late 1940 additional armor was bolted on to the hull and superstructure.