of the mine and its unusual shape meant that the bomb-bay doors had to be removed and the mine hung partly below the fuselage. It was mounted on two crutches and before dropping it was spun by an auxiliary motor. Chadwick also worked out the design and installation of controls and gear for the carriage and release of the mine in conjunction with Barnes Wallis. The Avro Lancaster B Mk IIIs so modified were known as Lancaster B Mark III Special (Type 464 Provisioning).

In February 1943, Air Vice-Marshal Francis Linnell