The large, graceful Sunderland was among World War II’s best flying boats. Because it bristled with armament, the Germans regarded it as the “Flying Porcupine.”
The advent of successful Short Empire C-class flying boats in 1933 persuaded the British Air Ministry to consider its adoption for military purposes. That year it issued Specification R. 2/33 to replace the aging biplane flying boats with a new monoplane craft. The prototype Sunderland was heavily based upon the civilian craft when it first flew in 1937. It was a high-wing, four-engine airplane with stressed-skin construction and a very deep, two-step hull. The spacious hull of the Sunderland allowed for creature comforts not associated with military craft. These included comfortable bunks, wardrooms, and a galley serving hot food, all of which mitigated the effects of 10-hour patrols. The craft was also the first flying boat fitted with powered gun turrets in the nose, dorsal, and tail positions, as well as the first to carry antishipping radar. Despite its bulk, the Sunderland handled well in both air and water and became operational in 1938. World War II commenced the following year, and Sunderlands ultimately equipped 17 Royal Air Force squadrons.
This capable aircraft played a vital role in the ongoing battles in the Atlantic. They cruised thousands of miles over open ocean, providing convoy escorts and attacking U-boats whenever possible. The first submarine kill happened in January 1940 when a Sunderland forced the scuttling of U-55. The big craft, by flying low to the water, could also defend itself handily. On several occasions, Sunderlands beat off roving bands of Junkers Ju 88s with considerable loss to the attackers. The Germans held the big craft in such esteem that they nicknamed it the Stachelschwein (Porcupine). Sunderlands performed useful service in the Atlantic and Pacific theaters throughout the war.
Steady improvements through Mks. I-V improved the aircraft’s performance in the air, though at some disadvantage in water handling. With a speed of 165 mph and a payload of just under 10,000 pounds, the aircraft had a range of about 1,000 miles. The aircraft was primarily used in long (10-12-hour) patrol and reconnaissance missions, including convoy protection and U-boat searches, as well as some search and rescue. Sunderland production stopped with 749 built (456 were Mk. III) by the end of World War II, though the type would remain in service in Britain to 1957 and elsewhere through 1967. An improved model, the S. 45 Seaford, was designed, but only a handful were built. Three dozen copies of both models were converted for postwar civil use.
The protection of our returning vessels was not the only service rendered by the Royal Air Force during the Greece 1941 evacuation. An emergency ‘air lift’ for ‘V. I. P. s’, Headquarters parties, and the like was organized by No. 201 Group at Alexandria. The aircraft employed were the Sunderlands of Nos. 228 and 230 Squadrons, which carried out reconnaissance by day and evacuation by night, the Lodestars and Bombays of No. 267 (Communications) Squadron, and two B. O. A. C. flying-boats. The Lodestars and Bombays mad only five trips to Greece before conditions at Menidi and Eleusis made further flights impossible; thereafter, with the two B. O. A. C. aircraft, they concentrated on the Crete-Egypt section of the run. 3 But the Sunderlands made full use of their ability to alight at remote spots along the coast-one of them was attracted to a stranded party by signals from a shaving-mirror-and between them they succeeded in bringing off from Greece nearly nine hundred persons. The King of Greece and most of our senior commanders mad their exit this way; a little earlier in King Peter had been rescued in similar fashion from Yugoslavia. Needless to say, the pilots took on fantastic loads. One Sunderland with an official ’emergency capacity’ of thirty bodies staggered off the water with eighty-four.
The most dramatic aircraft to fly into Berlin proved to be the Sunderland flying boats of the British Coastal Command. Taking off from Finkenwerder on the Elbe River near Hamburg they landed on the Havel See in Berlin with nine tons of cargo to be met by Berliners paddling out in boats with flowers like some scene from a South Pacific travelogue film. Crews for the British planes came not only from the United Kingdom, but also from India, Australia, New Zealand, and South Africa.
The first S.25, now named the Sunderland Mark I, flew from the River Medway on 16 October 1937 with Shorts’ Chief Test Pilot, John Lankester Parker at the controls. The deeper hull and installation of nose and tail turrets gave the Sunderland a considerably different appearance from the Empire flying boats. The prototype was fitted with Bristol Pegasus X engines, each providing 950 hp (709 kW ), as the planned Pegasus XXII engines of 1,010 hp (753 kW) were not available at the time.
The 37 mm gun, originally intended as a primary anti-submarine weapon, was dropped from the plans during the prototype phase and replaced with a Nash & Thomson FN-11 nose turret mounting a single .303 inch (7.7 mm) Vickers GO machine gun. The turret could be winched back into the nose, revealing a small “deck” and demountable marine bollard used during mooring manoeuvres on the water. The change of armament in the nose to the much lighter gun moved the centre of gravity rearwards.
After the first series of flights the aircraft was returned to the workshop and the wing was swept 4.25° to the rear, thereby moving the centre of pressure into a more reasonable position in relation to the new centre of gravity. This left the engines and wing floats canted out from the aircraft’s centreline. Although the wing loading was much higher than that of any previous Royal Air Force flying boat, a new flap system kept the takeoff run to a reasonable length and the aircraft first flew with the new wing sweep and the uprated Pegasus XXII engines on 7 March 1938.
Official enthusiasm for the type had been so great that in March 1936, well before the first flight of the prototype, the Air Ministry ordered 21 production examples. Meanwhile, delivery of the other contender Saro A.33 was delayed and it did not fly until October 1938. The aircraft was written off after it suffered structural failure during high speed taxi trials and no other prototypes were built.
Sunderland Mark I
The RAF received its first Sunderland Mark I in June 1938 when the second production aircraft (L2159) was flown to 230 Squadron at RAF Seletar, Singapore. By the outbreak of war in Europe, in September 1939, RAF Coastal Command was operating 40 Sunderlands.
The main offensive load was up to 2,000 lb (910 kg) of bombs (usually 250 or 500 lb), mines (1,000 lb) or other stores that were hung on traversing racks under the wing centre section (to and from the bomb room in the fuselage). Later, depth charges (usually 250 lb) were added. By late 1940, two Vickers K machine guns had been added to new hatches that were inserted into the upper sides of the fuselage just aft of the wing, with appropriate slipstream deflectors. A second gun was added to the nose turret. New constant speed propellers and deicing boots were installed as well during 1940.
The Sunderland had difficult in landing and taking off from rough water, but, other than in the open sea, it could be handled onto and off a short chop, by a skilled pilot. Many rescues were made, early in the war, of crews that were in the Channel having abandoned or ditched their aircraft, or abandoned their ship. In May 1941, during the Battle of Crete Sunderlands transported as many as 82 armed men from place to place in one load. Steep ocean swells were never attempted, however a calm ocean could be suitable for landing and takeoff.
Beginning in October 1941, Sunderlands were fitted with ASV Mark II “Air to Surface Vessel” radar. This was a primitive low frequency radar system operating at a wavelength of 1.5 m. It used a row of four prominent “stickleback” yagi antennas on top of the rear fuselage, two rows of four smaller aerials on either side of the fuselage beneath the stickleback antennas, and a single receiving aerial mounted under each wing outboard of the float and angled outward.
A total of 75 Sunderland Mark Is were built: 60 at Shorts’ factories at Rochester and Belfast, Northern Ireland, and 15 by Blackburn Aircraft at Dumbarton.
Sunderland Mark II
In August 1941, production moved on to the Sunderland Mark II which used Pegasus XVIII engines with two-speed superchargers, producing 1,065 hp (794 kW) each.
The tail turret was changed to an FN.4A turret that retained the four .303 guns of its predecessor but provided twice the ammunition capacity with 1,000 rounds per gun. Late production Mark IIs also had an FN.7 dorsal turret, mounted offset to the right just behind the wings and fitted with twin .303 machine guns. The hand held guns behind the wing were removed in these versions.
Only 43 Mark IIs were built, five of these by Blackburn.
Sunderland Mark III
Production quickly changed in December 1941 to the Sunderland Mark III which featured a revised hull configuration which had been tested on a Mark I the previous June. This modification improved seaworthiness, which had suffered as the weight of the Sunderland increased with new marks and field changes. In earlier Sunderlands, the hull “step” that allows a flying boat to “unstick” from the surface of the sea was an abrupt one, but in the Mk III it was a curve upwards from the forward hull line.
The Mark III turned out to be the definitive Sunderland variant, with 461 built. Most were built by Shorts at Rochester and Belfast, a further 35 at a new (but temporary)[N 3] Shorts plant at White Cross Bay, Windermere; while 170 were built by Blackburn Aircraft. The Sunderland Mark III proved to be one of the RAF Coastal Command’s major weapons against the U-boats, along with the Consolidated PBY Catalina.
As the U-boats began to use Metox passive receivers the ASV Mk II radar gave away the presence of aircraft and the number of sightings diminished drastically. The RAF response was to upgrade to the ASV Mk III, which operated in the 50 cm band, with antennas that could be faired into fewer more streamlined blisters. During the Mk III’s life there were a large number of almost continuous improvements made, including the ASV Mk IIIA and four more machine guns in a fixed position in the wall of the forward fuselage just behind the turret (developed on RAAF aircraft first) with a simple bead and ring sight for the pilot.
Despite the 14-hour-long patrols expected of their crews, early Sunderland gunners were provided with only 500 rounds of ammunition each. Later 1,000 round ammunition boxes were installed in the turrets. The beam hatch guns were removed from Mk II aircraft but Mk IIIs and then Mk Is gained much more capable .50 inch (12.7 mm) guns, one each side.
Offensive weapons loads increased too. The introduction of the hydrostatically fused 250 lb (110 kg) depth charge meant that additional weapons could be carried on the floor of the bomb room in wooden restraints, along with ammunition boxes of 10 and 25 lb anti-personnel bombs that could be hand launched from various hatches to harass U-boat crews otherwise manning the twin 37 and dual quadruple 20 mm cannons with which U-boats were fitted.
As radar detection became more effective there were more night patrols to catch U-boats on the surface charging their batteries. Attacking in the dark was a problem that was solved by carrying one inch (25.4 mm), electrically initiated flares and dropping then out of the rear chute of the aircraft as it got close to the surface vessel. Sunderlands were never fitted with Leigh lights.
Sunderland Mark IIIa
The Sunderland Mark IIIa was more of an “evolution” of the Mark III with no documentation to define exactly which features were included. Photos of the Mark IIIa suggest varying numbers of bomb door windows and either the original Bristol Pegasus or the newer Pratt & Whitney engines.
ML883 of RCAF Squadron 423 was a Mk IIIa with the following features:
Bristol Pegasus XVIII engines
Two windows per bomb door (while ML422 was another Mk IIIa but with three windows per bomb door)
Radar blisters under the wingtips
Four additional fixed machine guns just aft of the forward turret.
Sunderland Mark IV
The Sunderland Mark IV was an outgrowth of the 1942 Air Ministry Specification R.8/42, for a generally improved Sunderland with more powerful Bristol Hercules engines, better defensive armament and other enhancements. The new Sunderland was intended for service in the Pacific. Although initially developed and two prototypes built as the “Sunderland Mark IV” it was different enough from the Sunderland line to be given a different name, the S.45 “Seaford”.
Relative to the Mark III, the Mark IV had a stronger wing, larger tailplanes and a longer fuselage with some changes in hull form for better performance in the water. The armament was heavier with .50 inch (12.7 mm) machine guns and 20 mm Hispano cannon.
The changes were so substantial that the new aircraft was redesignated the Short Seaford. Thirty production examples were ordered; the first delivered too late to see combat and only eight production Seafords were completed and never got beyond operational trials with the RAF.
Sunderland Mark V
The next production version was the Sunderland Mark V, which evolved out of crew concerns over the lack of power of the Pegasus engines. The weight creep (partly due to the addition of radar) that afflicted the Sunderland had resulted in running the Pegasus engines at combat power as a normal procedure and the overburdened engines had to be replaced regularly.
Australian Sunderland crews suggested that the Pegasus engines be replaced by Pratt & Whitney R-1830 Twin Wasp engines. The 14-cylinder engines provided 1,200 hp (895 kW) each and were already in use on RAF Consolidated Catalinas and Douglas Dakotas, and so logistics and maintenance were straightforward. Two Mark IIIs were taken off the production lines in early 1944 and fitted with the American engines. Trials were conducted in early 1944 and the conversion proved all that was expected. The new engines with new featherable propellors provided greater performance with no real penalty in range. In particular, a Twin Wasp Sunderland could stay airborne if two engines were knocked out on the same wing while, in similar circumstances, a standard Mark III would steadily lose altitude. Production was switched to the Twin Wasp version and the first Mark V reached operational units in February 1945. Defensive armament fits were similar to those of the Mark III, but the Mark V was equipped with new centimetric ASV Mark VI C radar that had been used on some of the last production Mark IIIs as well.
A total of 155 Sunderland Mark Vs were built with another 33 Mark IIIs converted to Mark V specification. With the end of the war, large contracts for the Sunderland were cancelled and the last of these flying boats was delivered in June 1946, with a total production of 777 aircraft completed.
Sunderland III of Aquila Airways at Hamble Beach in 1955. This aircraft was the first transport conversion that had served BOAC 1943-1948, it still carried the name given to it by BOAC Hadfield.
In late 1942, the British Overseas Airways Corporation (BOAC) obtained six Sunderland Mark IIIs, which had been de-militarised on the production line, for service as mail carriers to Nigeria and India, with accommodation for either 22 passengers with 2 tons of freight or 16 passengers with 3 tons of freight. Armament was removed, the gun positions being faired over, and simple seating fitted in place of the bunks. As such they were operated by BOAC and the RAF jointly from Poole to Lagos and Calcutta. Six more Sunderland IIIs were obtained in 1943. Minor modifications to the engine angles and flight angle resulted in a significant increase in the cruise speed, which was a relatively unimportant issue for the combat Sunderlands. In late 1944, the RNZAF acquired four new Sunderland Mk IIIs already configured for transport duties. In the immediate postwar period, these were used by New Zealand’s National Airways Corporation to link South Pacific Islands in the “Coral Route” before TEAL Short Sandringhams took over after 1947.
BOAC obtained more Mark IIIs and gradually came up with better accommodation for 24 passengers, including sleeping berths for 16. These conversions were given the name Hythe and BOAC operated 29 of them by the end of the war. In February 1946, the first of these, G-AGJM, made a 35,313 mile route survey from Poole to Australia, New Zealand, Hong Kong, Shanghai and Tokyo in 206 flying hours. It was the first British civil flying boat to visit China and Japan.
A more refined civilian conversion of the Sunderland was completed by the manufacturer as the postwar Short Sandringham. The Sandringham Mk. I used Pegasus engines while the Mk. II used Twin Wasp engines.