The Short Sunderland III was produced in larger numbers than any other version of the aircraft, accounting for 463 of the total of 749 Sunderlands that were built. The main change introduced on the Mk III was the use of a faired main step on the bottom of the fuselage. This reduced the drag caused by the boat hull by ten percent, but did have some impact on the aircraft’s handling in water.
The prototype Mk III, a converted Mk I, made its first flight on 28 June 1941, and the first production aircraft flew on 15 December 1941. At first the Mk III was very similar to the Mk II, with the same guns and ASV II radar. Early in 1943 ASV.Mk III radar was installed. This was based on the centimetric H2S radar used by Bomber Command, and unlike the ASV II radar could not be detected by the U-boats. The last batch of Sunderland IIIs was given ASV.Mk IVc radar, which replaced the Yagi aerials with under-wing split scanners in protective radomes. Later Sunderland IIIs were also give a battery of four fixed 0.303in machine guns in the nose, to counter the increasingly powerful anti-aircraft armament carried by the U-boats.
The Sunderland III was produced at all four factories involved in Sunderland production – 186 were produced by Shorts at Rochester, 35 on Windermere and the rest at Belfast and Dumbarton. The Mk III was the last significant version of the Sunderland – the Mk IV evolved into the Seaford and never entered service, while the Mk V did not appear until 1945, by which time the battle of the Atlantic had been won.
Engine: Four Bristol Pegasus XVIII
Span: 112ft 9in
Length: 85ft 4in
Height: 34ft 6in
Max speed: 210mph
Loaded Weight: 58,000lb
Armament: Two 0.303in in nose turret, four in tail turret and three in dorsal turret; four fixed 0.303in guns added to nose in later aircraft
Bomb load: 2,000lb on retractable racks