The Avro Shackleton is a British long-range maritime patrol aircraft (MPA) which was used by the Royal Air Force (RAF) and the South African Air Force (SAAF). It was developed by Avro from their Lincoln bomber, which itself had been a development of the famous wartime Lancaster bomber.
The Shackleton was developed during the late 1940s as part of Britain's military response to the rapid expansion of the Soviet Navy, in particular its submarine force. Produced as the primary type equipping RAF Coastal Command, the Type 696 as it was initially designated, incorporated major elements of the Lincoln, as well as the Avro Tudor airliner, and was furnished with an extensive electronics suite in order to perform the anti-submarine warfare (ASW) mission, along with much-improved crew facilities due to the long mission times involved in patrol work. The type was named Shackleton, after the polar explorer Sir Ernest Shackleton.
The Shackleton entered operational service with the RAF in April 1951 and was used primarily in the ASW and MPA roles, but it was also frequently deployed as an aerial search and rescue (SAR) platform and for performing several other secondary roles such as mail delivery and as an ad-hoc cargo and troop-transport aircraft. In addition to its service with the RAF, South Africa also procured the Shackleton to equip the SAAF. In South African service, the type was operated in the maritime patrol capacity between 1957 and 1984. During March 1971, a number of SAAF Shackletons were used during the SS Wafra oil spill, intentionally sinking the stricken oil tanker using depth charges to prevent further ecological contamination.
During the 1970s, the Shackleton was replaced in the maritime patrol role by the jet-powered Hawker Siddeley Nimrod, however a small number of the RAF's existing Shackletons received extensive modifications in order to adapt them to perform the airborne early warning (AEW) role. The type continued to be used in this role until 1991, when it was replaced by the Boeing E-3 Sentry AEW aircraft. These were the last examples of the type remaining in active service.
Development Origins The Battle of the Atlantic was a crucial element of the Second World War, in which Britain sought to protect its shipping from the German U-boat threat. The development of increasingly capable diesel-electric submarines had been rapid, and in particular the snorkel virtually eliminated the need for submarines to surface while on patrol. Aircraft that had once been highly effective submarine-killers had very quickly become incapable in the face of these advances.Jefford et al. 2005, pp. 67–68. In addition, lend-leased aircraft such as the Consolidated B-24 Liberator had been returned following the end of hostilities. Several Avro Lancasters had undergone rapid conversion (designated Maritime Reconnaissance Mk 3 (MR3)) as a stopgap measure for maritime search and rescue and general reconnaissance duties;Jones 2002, pp. 22, 27. however, RAF Coastal Command had diminished to only a third of its size immediately after the Second World War.Jefford et al. 2005, pp. 68–69.
In the emerging climate of the Cold War, and the requirement to guard the North Atlantic from an anticipated rapid expansion of the Soviet Navy's submarine force, a new aerial platform to perform the anti-submarine mission was required.Jones 2002, p. 43. Work had begun on the requirement for a new maritime patrol aircraft in 1944, at which point there had been an emphasis on long-range platforms for Far East operations. However, with the early end of the war in the Pacific, the requirement was refined considerably. In late 1945, the Air Staff had expressed interest in a conversion of the Avro Lincoln as a general reconnaissance and air/sea rescue aircraft, formalising their requirements for such an aircraft under Air Ministry specification R.5/46. Avro's Chief Designer Roy Chadwick initially led the effort to build an aircraft to this requirement, designated as the Avro Type 696.Billings, Bill. "The Shackleton Story." The Shackleton Association. Retrieved: 10 July 2008.
The Type 696 was a significant development of the Lincoln. Elements of the Avro Tudor airliner were also reused in the design, both the Lincoln and the Tudor being derivatives of the successful wartime Lancaster bomber.Buttler 2004, p. 144.Jones 2002, p. 30. Crucially, the new aircraft was to be capable of a range while carrying up to of weapons and equipment. In addition to featuring a large amount of electronic equipment, the Type 696 provided a much-improved crew environment compared to other aircraft types, to allow the crew to be more effective during the anticipated lengthy mission times.Jefford et al. 2005, pp. 70–71.Flight 18 May 1950, p. 611. During development the Type 696 was provisionally referred to as the Lincoln ASR.3 before the official name 'Shackleton' was selected.
The first test flight of the prototype Shackleton GR.1, serial VW135, was made on 9 March 1949 from the manufacturer's airfield at Woodford, Cheshire in the hands of Avro's Chief Test Pilot J.H. "Jimmy" Orrell.Harlin and Jenks 1973, p. 164. The GR.1 was later redesignated "Maritime Reconnaissance Mark I" (MR 1). The prototype differed from subsequent production Shackletons in a number of areas, featuring several gun turrets and was equipped for air-to-air refuelling using the looped-line method. These did not feature on production aircraft due to performance difficulties or being judged ineffective.Jones 2002, pp. 34, 36–37, 39. However, the performance of the prototype had been such that in addition to the go-ahead for the MR1's production, a specification for an improved variant was issued in December 1949, before the first production Shackleton had even flown.Jefford et al. 2005, pp. 71–74. By 1951, the MR1 had become officially considered as an interim type due to several shortcomings.Jones 2002, p. 67.
Further development
The MR 2 was an improved version of the Shackleton, featuring numerous refinements that had been proposed for the MR1. The radar was upgraded to ASV Mk 13, and the radome relocated from the aircraft's nose to a ventral position aft of the bomb bay, the radome was retractable and could be fully extended only with the bomb bay doors open. It had improved all round radar coverage and minimised the risk of bird strikes.World Aircraft Information Files 1997. Both the nose and tail section were lengthened, the tailplane was redesigned, the undercarriage was strengthened and twin-retractable tailwheels were fitted. The Bristol dorsal turret was initially retained, but was later removed from all aircraft after delivery.Jefford et al. 2005, pp. 74–75. The prototype, VW126, was modified as an aerodynamic prototype at the end of 1950 and first flew with the MR 2 modification on 19 July 1951.
VW126 was tested at Boscombe Down in August 1951, particular attention being paid to changes made to improve its ground handling, such as the addition of toebrakes and a lockable rudder system. One production Mk 1 aircraft was modified on the line at Woodford with the Mk 2 changes and first flew on 17 June 1952. After the trials were successful, it was decided to complete the last ten aircraft being built under the Mk 1 contract to MR 2 standard and further orders were placed for new aircraft. In order to keep pace with changing submarine threats, the Mk 2 force was progressively upgraded, with Phase I, II and III modifications introducing improved radar, weapons and other systems, as well as structural work to increase fatigue life. Production of the MR 2 ended in May 1954.Jones 2002, p. 85.
The Type 716 Shackleton MR 3 was another redesign in response to crew feedback and observations. A new tricycle undercarriage was introduced, the fuselage was increased in all main dimensions and had new wings with better ailerons and tip tanks.Jones 2002, pp. 93, 95–96. The weapons capability was also upgraded to include homing torpedoes and Mk 101 Lulu nuclear depth bombs. To reduce crew fatigue on 15-hour flights, the sound deadening was improved and a proper galley and sleeping space were included. Due to these upgrades, the takeoff weight of the RAF's MR 3s had risen by over 30,000 lb (13,600 kg) (Ph. III) and assistance from Armstrong Siddeley Viper Mk 203 turbojets was needed on takeoff with a 5-minute limit. The Griffons had to be run at high power for very long periods after a heavyweight take-off so the Vipers were later cleared to run for four hours continuously so lower Griffon power settings could be used which reduced the risk of failures.The Shackleton, Chris Ashworth, Aston Publications Limited 1990, , p.44"Shackletons in the SAAF – Retirement." The Shackleton Project. Retrieved: 10 July 2008.Jefford et al. 2005, pp. 77–78. The extra strain took a toll on the airframe, and flight life of the RAF MR 3s was so reduced that they were outlived by the MR 2s. Due to the arms embargo against South Africa, the SAAF's MR 3s never received these upgrades but were maintained independently by the SAAF.
The Type 719 Shackleton IV, later known as the MR 4, was a projected variant intended to meet a Canadian requirement for a long-range patrol aircraft. The MR 4 would have been practically a new aircraft, sharing only the nose, cockpit, and outer wings with earlier variants; it would have also been powered by the Napier Nomad compound engine.Jefford et al. 2005, p. 88. The Shackleton IV was cancelled in 1955, the Canadian requirement being subsequently met by the Britannia Maritime Reconnaissance, based on the Bristol Britannia airliner, later entering production as the Canadair Argus.
In 1967, ten MR 2s were modified as training aircraft to replace the T 4 in-service with the Maritime Operational Training Unit. Known as T 2s, the crew rest areas were replaced by additional radar equipment and the original radar fittings removed.Jones 2002, pp. 84–85.
Design
The Shackleton was a purpose-built aircraft for the maritime patrol role; however, the legacy of Avro's preceding aircraft is present in many aspects of the overall design. The centre section of the Shackleton's wing originates from the Lincoln, while the outer wing and undercarriage were sourced from the Tudor. At one stage during development the tailplane had closely resembled the Lincoln's but was enlarged and changed soon after. An entirely new fuselage was adopted, being wider and deeper to provide a large space in which to accommodate the crew, their equipment, and a large bomb bay.Jefford et al. 2005, p. 72.Jones 2002, p. 31. Later variants of the Shackleton were substantially redesigned, adopting a nosewheel undercarriage, redesigned wings and centre-section, and a larger fuel capacity for more range.Jefford et al. 2005, p. 76.
Various armaments and equipment were carried by the Shackleton in order to perform its missions. In ASW operations, the ASV Mk 13 radar was the primary detection tool. It could detect a destroyer at a range of , a surfaced submarine at , and a submarine's conning tower at , although rough seas considerably reduced the radar's effectiveness.Jones 2002, p. 34. Other equipment included droppable sonobuoys, electronic warfare support measures and an Autolycus diesel fume detection system. A special camera bay housed several reconnaissance cameras capable of medium altitude and nighttime vertical photography and low-altitude oblique photography. The crew would also perform visual searches using various lookout positions that were provided for this purpose.Flight 18 May 1950, p. 617. Weapons carried included up to nine bombs, three homing torpedoes or depth-charges. The aircraft also had two 20 mm cannon in a Bristol dorsal turret. An in-flight refueling receptacle could be accommodated, but was not fitted on production aircraft.Jefford et al. 2005, pp. 72–74.