Short Sunderland

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Sunderland
Type	Military flying boat
Manufacturer	Short Brothers
Maiden flight	16 October 1937
Retired	1967
Primary users	RAF RAAF RNZAF French Naval Air Service (Aéronavale)
Variants	Short Sandringham

The S.25 Sunderland was a British flying boat patrol bomber developed for the Royal Air Force by Short Brothers, first flown on 16 October 1937. Based in part upon the S.23 Empire flying boat, the flagship of Imperial Airways, the S.25 was extensively re-engineered for military service. As one of the most powerful and widely used flying boats throughout the Second World War, it terrorized the German U-boat fleet. It was named for the town of Sunderland in northeast England.

Contents 1 Design and development 1.1 Basic design 2 Variants 2.1 Prototype 2.2 Sunderland Mark I 2.3 Sunderland Mark II 2.4 Sunderland Mark III 2.5 Sunderland Mark IV (S.45 Seaford) 2.6 Sunderland Mark V 3 Operational history 3.1 World War II 3.2 Post-War 4 Transport variants—Hythe and Sandringham 5 Military Operators 5.1 Australia 5.2 Canada 5.3 France 5.4 New Zealand 5.5 Norway 5.6 South Africa 5.7 United Kingdom 6 Commercial operators 7 Specifications (Sunderland III) 8 Reference 9 External links 10 Related content

[edit] Design and development

The early 1930s saw intense competition in developing long-range flying boats for intercontinental passenger service. The United Kingdom had no match for the new American Sikorsky S-42 flying boats, which were making headlines all over the world. The powers-that-be in Britain felt that "something should be done".^{[citation needed]}

In 1934, the British Postmaster General declared that all first-class Royal Mail sent overseas was to travel by air, effectively establishing a subsidy for the development of intercontinental air transportation in a fashion similar to the U.S.'s domestic program a decade earlier. In response, Imperial Airways announced a competition between aircraft manufacturers to design and produce 28 flying boats, each weighing 18 tons (18.2 tonnes) and having a range of 700 miles (1,130 km) with a capacity for 24 passengers.

The contract went almost directly to Short Brothers of Rochester, England. Although Short had long built flying boats for the military and for Imperial Airways, none of them were in the class of size and sophistication requested, but the business opportunity was too great to pass up. Oswald Short, head of the company, began a fast-track program to come up with a design for a flying boat far beyond anything they had ever built.

While the first S.23 was under development, the British military was taking actions that would result in a purely military version of the big Shorts flying boats. The 1933 Air Ministry requirement "R.2/33" called for a next-generation flying boat for ocean reconnaissance, in which the new aircraft had to have four engines but could be either a monoplane or biplane design.

The R.2/33 specification was released roughly in parallel with the Imperial Airways requirement, and while Shorts continued to develop the S.23, they also worked on a response to the Air Ministry's need at a lower priority. The military flying boat variant was designated S.25 and the design was submitted to the Air Ministry in 1934. Saunders-Roe also designed a flying boat, designated the "A.33", in response to the R.2/33 competition, and prototypes of both the S.25 and A.33 were ordered by the Ministry for evaluation.

[edit] Basic design

The S.25 shared much in common with the S.23 but was most notably different in that it had a deeper hull profile. As with the S.23, the Sunderland's fuselage contained two decks with six bunks on the lower one, a galley with a twin kerosene pressure stove, a yacht-style porcelain flush toilet, an anchoring winch and a small machine shop for in-flight repairs. The crew was originally intended to be seven but increased in later versions to 11 or more.

It was of all-metal construction except for most of the control surfaces that were of fabric-covered metal-frame construction. Portable beaching gear could be attached by ground crew so that the aircraft could be pulled up on land (beached). The gear consisted of two 2-wheeled struts that could be attached to either side of the fuselage, below the wing, with a 2- or 4-wheel trolley and tow bar that could be attached under the rear of the hull.

The thick wings carried the four nacelle-mounted Bristol Pegasus XXII engines and accommodated six drum fuel tanks with a total capacity of 9,200 l (2,025 Imperial gallons, 2,430 US gallons). Four smaller fuel tanks were added later behind the rear wing spar to give a total fuel capacity of 11,602 l (2,550 Imperial gallons, 3,037 US gallons), enough for 8- to 14-hour patrols.

The specification called for an offensive armament of a 37-mm gun and up to 2,000 pounds (900 kg) of bombs, mines or (eventually) depth charges. The ordnance was stored inside the fuselage and was winched up to racks, under the wing centre-section, that could be traversed out through doors on each side of the (bomb room) fuselage above the waterline to their offensive position. Defensive armament included a Nash & Thomson FN-13 powered turret with four .303 Browning machine guns in the extreme tail and a manually operated .303 on either side of the fuselage, firing from ports just below and behind the wings.

[edit] Variants

[edit] Prototype

The first S.25, now named the Sunderland Mark I, flew from the River Medway on 16 October 1937. 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 709 kW (950 hp), as the planned Pegasus XXII engines of 753 kW (1,010 hp) 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 0.303 inch (7.7 mm) Vickers GO machine gun. The turret could be winched back into the nose, revealing a small "deck" and de-mountable 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 flight, the aircraft was returned to the shop and a modified wing was installed with a 4.5° sweep 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 RAF flying boat, a new flap system kept the take-off run to reasonable length, and the aircraft first flew with the new wing and the uprated Pegasus XXII engines on March 7, 1938.

Official enthusiasm for the type was so great that in March 1936, before the first flight of the prototype, the Air Ministry had ordered 21 production examples.

Meanwhile, delivery of the SaRo A.33 was delayed and it did not fly until October 1938. The aircraft was written off after it suffered a structural failure during high-speed taxi trials and no other prototypes were built.

[edit] Sunderland Mark I

The RAF received its first Sunderland Mark I in June 1938 when the second production aircraft was flown to Singapore. By the outbreak of war in Europe, in September 1939, RAF Coastal Command was operating 40 Sunderlands.

Beginning in October 1941, Sunderlands were fitted with ASV Mark II radar (Anti-Surface Vessel). This was a primitive low-frequency radar system operating at a wavelength of 1.5 m, featuring 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, England and Belfast, Northern Ireland, and 15 by Blackburn Aircraft at Dumbarton.

[edit] Sunderland Mark II

In August 1941, production moved to the Sunderland Mark II that featured Pegasus XVIII engines with two-speed superchargers, providing 794 kW (1,065 hp) each.

The tail turret was changed to an FN.4A turret that retained the four .303 (7.7 mm) guns of its predecessor but provided twice the ammunition capacity with 1,000 rounds per gun. Late production Mark IIs also had a FN.7 dorsal turret, mounted offset to the right just behind the wings and fitted with twin .303 (7.7 mm) machine guns. The hand-held guns behind the wing were removed in these versions.

Only 43 Mark IIs were built, with five manufactured by Blackburn.

[edit] Sunderland Mark III

Production quickly went on in December 1941 to the Sunderland Mark III, which featured a revised hull configuration as 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^[1]) Shorts plant at White Cross Bay, Lake Windermere^[2][3]; 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.

[edit] Sunderland Mark IV (S.45 Seaford)

Although a Sunderland Mark IV was developed it proved to be different enough from the Sunderland line to be given a different name and did not see combat. The Sunderland Mark IV was an outgrowth of a 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.

Relative to the Mark III, the Mark IV had a stronger wing, bigger tailplanes and a longer fuselage with some changes in form. The armament was greatly improved, consisting of two fixed forward-firing .50 calibre (12.7 mm) machine gun in the nose, a Brockhouse nose turret with twin .50 calibre (12.7 mm) machine guns, twin 20 mm Hispano cannon mounted in a B-17 Flying Fortress dorsal turret, twin .50 calibre (12.7 mm) guns in a Martin tail turret and another .50 calibre (12.7 mm) machine gun in a hand-held position on each side of the fuselage,

The changes were so substantial that the new aircraft was redesignated the S.45 Seaford. Two prototypes and 30 production examples were ordered, and the first prototype flew in April 1945, well after the introduction of the Sunderland IV, and too late to see combat. The prototypes were powered by Hercules XVII engines with 1,253 kW (1,680 hp), but production aircraft used Hercules XIXs with 1,283 kW (1,720 hp). Only eight production Seafords were completed and never got beyond operational trials with the RAF.

The Sunderland was developed, via the Short Sandringham, into the Short Solent. The second production Seaford was loaned to BOAC in 1946 for evaluation as a civil airliner. BOAC liked it and 12 Seafords then being laid down were completed as Solent Mark IIs. Most of the RAF Seafords were rebuilt as Solent Mark IIIs.

[edit] 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 on a regular basis.

Australian Sunderland crews suggested that the Pegasus engines be replaced by Pratt & Whitney R-1830-9OB Twin Wasp engines. The 14-cylinder engines provided 895 kW (1,200 HP) each and were in use on RAF Consolidated Catalinas and Douglas Dakotas, making logistics and maintenance 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 (and 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.

One hundred and fifty-five Sunderland Mark Vs were built and another 33 Mark IIIs were converted to Mark V specification. With the end of the war, large contracts for the Sunderland were cancelled and the last of these great flying boats was delivered in June 1946, with a total production of 749 aircraft.

[edit] Operational history

[edit] World War II

During the Second World War, although British anti-submarine efforts were disorganized and ineffectual at first, Sunderlands quickly proved useful in the rescue of the crews from torpedoed ships. On 21 September 1939, two Sunderlands rescued the entire 34-man crew of the torpedoed merchantman Kensington Court from the North Sea. As British anti-submarine measures improved the Sunderland began to show its claws as well. A Royal Australian Air Force (RAAF) Sunderland performed the type's first unassisted kill of a U-boat on 17 July 1940.

As aircrew honed their combat skills, the Sunderland Mark I received various improvements to make it more effective. The nose turret was upgraded to two .303 (7.7 mm) guns instead of one, and new propellers together with pneumatic rubber wing de-icing boots were also fitted.

Although the .303 guns lacked range and hitting power, the Sunderland had a fair number of them and it was a well-built machine that was hard to destroy. On 3 April 1940, a Sunderland operating off Norway was attacked by six German Junkers Ju 88 light bombers and managed to shoot one down, damage another enough to send it off to a forced landing, and drove off the rest. The Germans are reported to have nicknamed the Sunderland the "Fliegendes Stachelschwein" (Flying Porcupine) due to its defensive firepower and to the several prominent antennas protruding from it.

Sunderlands also proved themselves in the Mediterranean theatre. They performed valiantly in evacuations during the German seizure of Crete, carrying a surprising number of passengers, and one performed the reconnaissance mission to observe the Italian fleet at anchor in Taranto before the famous Royal Navy Fleet Air Arm's torpedo attack on 11 November 1940, the Battle of Taranto.

New weapons made the flying boats more deadly in combat. The ineffectual anti-submarine bombs, which in some cases were known to bounce up and hit their launch aircraft, were replaced by early 1943 by much more effective Torpex depth charges that would sink to a predetermined depth and then explode. This eliminated the problem of bounce-back and the shock wave propagating through the water had greater effect.

Although the bright Leigh searchlight was rarely fitted to Sunderlands, ASV Mark II radar allowed the flying boats to effectively target U-boats operating on the surface. In response, the German submarines began to carry a radar warning system known as "Metox", also known as the Cross of Biscay due to the appearance of its receiving antenna that was tuned to the ASV frequency and gave the submarines early warning that an aircraft was in the area.

Kills fell off drastically until ASV Mark III radar was introduced in early 1943, which operated in the centimetric band and used antennas mounted in blisters under the wings outboard of the floats, instead of the cluttered stickleback aerials. Sunderland Mark IIIs fitted with ASV Mark III were designated Sunderland Mark IIIAs.

Centimetric radar was invisible to Metox and completely baffled the Germans at first. Admiral Karl Dönitz, commander of the German U-boat force, suspected at first that the British were being informed of submarine movements by spies. There is an unsubstantiated story that a British prisoner confused the Germans by claiming that the aircraft were homing in on the signals emanating from their own Metox system.^{[citation needed]}

In any case, the Germans responded by fitting U-boats with one or two 37 mm and twin quad 20 mm flak guns to shoot it out with the attackers. While Sunderlands could suppress flak to an extent by hosing down the U-boat with their nose-turret guns, the U-boats had the edge by far in range and hitting power. To help improve the odds, the Australians first fitted their aircraft, in the field, with an additional four .303s in fixed mounts in the nose, allowing the pilot to add fire while diving on the submarine before bomb release. Most aircraft were similarly modified. The addition of single .50 calibre (12.7 mm) flexibly-mounted M2 Browning machine guns in the (previously emptied) beam hatches behind and above the wing trailing edge also became common.

The rifle-calibre .303 guns were far from satisfactory as they lacked hitting power but the Sunderland retained its reputation for being able to take care of itself. This reputation was enhanced by a savage air battle between eight Ju 88C long-range heavy fighters and a single RAAF Sunderland Mark III on June 2, 1943. There were 11 crewmen on board the Sunderland, including nine Australians and two British. The crew was on an anti-submarine patrol and also searching for remains of BOAC Flight 777, an airliner that had left Gibraltar the day before and subsequently had been shot down over the Bay of Biscay.

In the late afternoon, one of the crew spotted the eight Ju 88s. Bombs and depth charges were dumped while the pilot, Walker, "redlined" the engines. Two Ju 88s made passes at the flying boat, one from each side, scoring hits while the Sunderland went through wild "corkscrew" evasive manoeuvres. The fighters managed to knock out one engine. On the third pass of the fighters, the top-turret gunner managed to shoot one down. Another Ju 88 disabled the tail turret but the next fighter that made a pass was bracketed by the top and nose turrets and shot down as well.

Still another fighter attacked, smashing the Sunderland's radio gear, wounding most of the crew in varying degrees and mortally wounding one of the side gunners. A Ju 88 tried to attack from the rear but the tail turret gunner had managed to regain some control over the turret and shot it down. The surviving fighters pressed home their attacks despite the losses. The nose gunner damaged one of the fighters and set one of its engines on fire. Two more of the attackers were also hit and the other two finally disengaged and departed. Luftwaffe records indicate these were the only two that made it back to base.

The Sunderland was a wreck. The crew threw everything they could overboard and nursed the aircraft back to the Cornish coast where Walker managed to land and beach it. The crew waded ashore, carrying their dead comrade, while the surf broke the Sunderland up. Walker received the Distinguished Service Order and several of the other crew received medals as well. Walker went on to a ground job while the rest of the crew was given a new Sunderland. That Sunderland and its crew disappeared without a trace over the Bay of Biscay two months later after reporting by radio that they were under attack by six Ju 88s.

[edit] Post-War

At the end of the Second World War, a number of new Sunderlands built at Belfast were simply taken out to sea and scuttled as there was nothing else to do with them. However, despite this indignity, there was plenty of life left in the Sunderland. In Europe it was removed from service relatively quickly. However, in the Far East, where well-developed runways were less common and large land-based maritime patrol aircraft like the new Avro Shackleton could not be used so easily, there was still a need for it, and it remained in service with the Far East Air Force at Singapore until 1959, and with the Royal New Zealand Air Force's No. 5 Squadron RNZAF and No. 6 Squadron RNZAF until 1967. A preserved RNZAF Sunderland is at the Museum of Transport and Technology, Auckland.

During the Berlin Airlift ten Sunderlands and two Hythes were used to transport goods—especially salt— from Finkenwerder on the Elbe near Hamburg to the isolated city, landing on the Havelsee lake beside RAF Gatow until it iced over.^[4] This is the only known operational use of flying boats within central Europe.

The French Aéronavale Escadrille 7FE, which received Sunderlands when it was formed in 1943 as No. 343 Squadron RAF, continued to operate them until December 1960, the last unit to operate Sunderlands in the Northern Hemisphere.^[5]

RAF Sunderlands also saw service in the Korean War^[6] with No. 209 Squadron RAF and with the Australian (RAAF) and New Zealand (RNZAF) Air Forces until the mid-1960s.^[7]

[edit] Transport variants—Hythe and Sandringham

In late 1942, the British Overseas Airways Corporation (BOAC) obtained six Sunderland Mark IIIs and modified them for service as mail carriers to Nigeria and India, with primitive accommodation for seven passengers. Armament was removed, with 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. By minor modifications to the engine angles and flight angle a significant increase in the cruise speed, a relatively unimportant issue for the combat Sunderlands, was achieved.

BOAC obtained more Mark IIIs and gradually came up with better accommodations 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.

Another civilian conversion of the Sunderland was the postwar Sandringham. The Sandringham Mark I used Pegasus engines while the Sandringham Mark II used Twin Wasp engines. Apparently most or all of the Sandringhams were modified from existing Sunderlands but details of the Sandringham are unclear.

[edit] Military Operators

[edit] Australia

• Royal Australian Air Force
  • No. 10 Squadron RAAF
  • No. 40 Squadron RAAF
  • No. 461 Squadron RAAF

[edit] Canada

• Royal Canadian Air Force
  • No. 422 Squadron RCAF
  • No. 423 Squadron RCAF
  • No. 461 Squadron RCAF

[edit] France

• French Navy, Aéronavale
  • No. 343 Squadron RAF, later Escadrille 7FE^[8]
  • Flottille 1FE
  • Flottille 7F
  • Flottille 27F
  • Escadrilles 12S
  • Escadrilles 50S
  • Escadrilles 53S

[edit] New Zealand

• Royal New Zealand Air Force
  • No. 5 Squadron RNZAF
  • No. 6 Squadron RNZAF
  • No. 490 Squadron RNZAF

[edit] Norway

• No. 330 Squadron RAF

[edit] South Africa

• South African Air Force
  • No. 35 Squadron SAAF

[edit] United Kingdom

• Royal Air Force
  • No. 88 Squadron RAF
  • No. 95 Squadron RAF
  • No. 119 Squadron RAF
  • No. 201 Squadron RAF
  • No. 202 Squadron RAF
  • No. 204 Squadron RAF
  • No. 205 Squadron RAF
  • No. 209 Squadron RAF
  • No. 210 Squadron RAF
  • No. 228 Squadron RAF
  • No. 230 Squadron RAF
  • No. 240 Squadron RAF
  • No. 246 Squadron RAF
  • No. 259 Squadron RAF
  • No. 270 Squadron RAF

[edit] Commercial operators

• Aerolineas Argentinas.
• Ansett Flying Boat Services flew the Sunderland and its Sandringham variant from Rose Bay on Sydney Harbour to Lord Howe Island until 10 September 1974^[9]
• Aquila Airways.
• BOAC.
• CAUSA.
• Dodero.
• DNL.
• National Airways Corporation of New Zealand.
• Qantas.
• TEAL.
• Trans Oceanic Airways.

[edit] Specifications (Sunderland III)

Data from Jane's Fighting Aircraft of World War II^[10]

General characteristics

• Crew: 8—11 (two pilots, radio operator, navigator, engineer, bomb-aimer, three to five gunners)
• Length: 85 ft 4 in (26.0 m)
• Wingspan: 112 ft 9½ in (34.39 m)
• Height: 32 ft 10½ in (10 m)
• Wing area: 1,487 ft² (138 m²)
• Empty weight: 34,500 lb (15,663 kg)
• Loaded weight: 58,000 lb (26,332 kg)
• Powerplant: 4× Bristol Pegasus XVIII nine-cylinder radial engines, 1,065 hp (794 kW) each

Performance

• Maximum speed: 210 mph (336 km/h) at 6,500 ft (1,980 m)
• Cruise speed: 178 mph (285 km/h) at 5,000 ft (1,525 m)
• Stall speed: 78 mph (125 km/h)
• Range: 1,780 mi (2,848 km)
• Service ceiling: 16,000 ft (4,880 m)
• Rate of climb: 720 ft/min (3.67 m/s)
• Wing loading: 39 lb/ft² (191 kg/m²)
• Power/mass: .018 hp/lb (.030 kW/kg)

Armament

• 8× .303 calibre machine guns
• various munitions, including bombs and depth charges, carried internally and winched out beneath the wings

[edit] Reference

The initial version of this article was based on a public domain article from Greg Goebel's Vectorsite.

1. ^ The agreement with the Friends of the Lake District for the factory to be constructed on Windermere was conditional on its being dismantled when no longer needed. This agreement was kept and not a trace exists of the factory which had once boasted some of the largest aircraft hangars in the World
2. ^ http://www.thewestmorlandgazette.co.uk/archive/display.var.235391.0.mystery_surrounds_reports.php The Westmoreland Gazette archives 2002-11-28
3. ^ http://www.aohg.org.uk/twww/industry3.html The Way We Were - Lakeland Industries
4. ^ The Berlin Blockade. Spiritus Temporis history community. Retrieved on January 28, 2007.
5. ^ Barnes and James, p.559.
6. ^ http://www.geocities.com/jkjustin/weston31.html Image of 4 Sunderlands over RAF Seletar, Singapore
7. ^ http://www.kiwiaircraftimages.com/sundland.html RNZAF Sunderlands
8. ^ Barnes & James, p.359.
9. ^ Kiwi Aircraft Images.
10. ^ Jane, Fred T. “The Short S-25 Sunderland.” Jane’s Fighting Aircraft of World War II. London: Studio, 1946. p. 137. ISBN 1 85170 493 0.

[edit] External links

• Fighting the U-boats: Short Sunderland
• Short Sunderland
• Video of static preserved exhibit at IWM Duxford: http://www.youtube.com/watch?v=pIG5xFUQpgI

[edit] Related content

Comparable aircraft

• Kawanishi H8K
• PBM Mariner
• PB2M Mars
• PB2Y Coronado
• Saro Lerwick

Designation sequence

Short Singapore - Short Sandringham - Short Seaford -Short Solent - S.25 (Sunderland) - Short Stirling - Short Golden Hind - Short Shetland- SB.1 - SA/4 (Sperrin) - SB/6 (Seamew)

Related lists

List of aircraft of the RAF

See also

• RAF Gatow