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.

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. 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; however, RAF Coastal Command had diminished to only a third of its size immediately after the Second World War.

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. 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.

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. Crucially, the new aircraft was to be capable of a 3,000-nautical-mile (3,500 mi; 5,600 km) range while carrying up to 6,000 pounds (2,700 kg) 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. 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. 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. 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. By 1951, the MR1 had become officially considered as an interim type due to several shortcomings.