The BT 400 torpedo bomb was a non-powered torpedo. It was dropped at low altitude in a straight line to the target. The drive was only the kinetic energy of torpedoes.
The novel discharge ammunition for the Fw 190 was in the spring of 1943 proposed by Benecke of the Department “Technical air defense”.
The main advantage of BT was the simple and cheap production (the body was made of cast iron, the rear sheet steel). For example, while for a normal air torpedo F5 2000 working hours were necessary, the BT could be made in 60 hours. He could something more explosives to carry, required because of non-existing drive little scarce resources and needed a total of about 240 kg less material.
The first experiments were in Niedersonthofener See in Kempten performed. The development of target devices, detonators and other items, however, has prevented the use of this weapon.
There were several sizes (BT 200, BT 400, BT 700 A, 700 B BT, BT 1000, BT 1850).