Avro Lancaster B.III (Special)

Known at the time as "Type 464 Provisioning", these twenty-three aircraft were the machines of Operation Chastise. The conversion was carried out at Woodford Aerodrome near Stockport, working day and night: the bomb bay doors were removed and replaced with Vickers-built struts to hold the Upkeep mine, driven by a hydraulic motor — fed by the pump that had previously served the mid-upper turret — to spin the weapon before release.

Lamps were fitted in the bomb bay and nose as a rudimentary height-measuring system that allowed accurate low flying at night. The mid-upper turret was removed to save weight and its gunner moved to the front turret, freeing the bomb aimer to help with map reading. The aircraft also carried VHF radios, normally reserved for fighters, so that the formation leader could direct the attack over the target. For the 1955 film The Dam Busters several stored B VIIs were returned to this original configuration.