Number 617 Squadron

The Aircraft

The aircraft used by 617 Squadron on the Dams Raid were special adaptations of the basic Avro Lancaster  BIII known as the Type 464 Provisioning. 

Modifications included the removal of the Fraser Nash FN50 power operated mid upper turret together with its associated equipment and ammunition.  The bomb doors together with the internal bomb racks were removed and fared over fore and aft

In place of the bomb bay, a recess was created in which the bomb was held between a pair of V-shaped side-swing calliper arms each fitted with a 20" diameter discs, which corresponded to two circular tracks, one at each end of the bomb.  Back spin was imparted to the bomb by friction generated between the driven discs and the circular tracks on the bomb.   The power to spin the bomb was provided by a Vickers-Jassey motor driving a belt  running in a groove of the starboard driven disc.  Hydraulic power originally used to power the mid-upper turret and bomb-bay doors was diverted to a hydraulic motor on the fuselage floor.  As the front gunner had to be in his turret during the attack to deal with flack guns on the dams stirrups were fitted to make him more comfortable and to keep his feet out of the bomb-aimers way.

A pair of spot lamps mounted one under the nose and the other in the belly were designed to point downwards and to the port side, where the Navigator looking through the cockpit blister could see them shinning on the surface of the water.  When the pools of light formed a figure of eight the aircraft was at exactly 60 feet.

On the advice of Flt/Lt Bone of the Radio Department of the Royal Aircraft Establishment (RAE) at Farnborough a final modification involved the installation of VHF Type 1143 radio sets, to improve communication between the aircraft when operating at low level.  The use of this type of radio enabled Gibson to direct the attack, which in turn led to the subsequent development of the role of Master Bomber, whose job it was to direct  the bombing of a main force attack and keep it on the aiming point.

The drive belt can be clearly seen in the accompanying photograph of Wing Commander Guy Gibson's Lancaster ED932/G, AJ-G.  The /G indicates that the aircraft should be kept under guard when on the ground.  The covers over the wheels are to protect the tyres from oil dropping from the engines above. 

The other dimension of the standard Lancaster BIII are as follows: