WELLINGTON MARK III: A prototype Vickers Wellington long-range bomber fitted with two Bristol Hercules 14-cylinder two-row sleeve-valve radials of at least 1,400 h.p. each. Flying alongside is one of the later Supermarine Spitfires fitted with Rolls-Royce Merlin III engine driving a De Havilland three-bladed variable-pitch airscrew.
Prototype Wellington III L4251, fitted with Bristol Hercules HE1SM engines, in company with a Spitfire.

Detail views of the Vickers 40mm cannon dorsal turret fitted to L4250. The stressed-skin fuselage section is seen at left, with an internal view of the turret installation at right.

Wellington II T2545 was converted from a Mk IC.

Wellington Mk II prototype L4250 after modification with twin fins and rudders to cure instability caused by the experimental Vickers 40mm cannon turret. The centre fuselage had to be rebuilt as a stressed-skin structure because the normal geodetic frame was too flexible to allow accurate sighting of the gun. Powered by Merlin Xs, L4250 had made its first flight on March 3, 1939.

The Frazer-Nash hydraulic front turret of a Mk II Wellington, showing the twin 0-303in Browning machine guns.

A close-up of a Rolls-Royce Merlin X engine in a Wellington II. The Merlin X was rated at 1,145 h.p.

The twin-Browning tail turret of a Wellington II. The turrets used a 300 lb/in hydraulic supply.

Wellington Mk II (special turret)