The aircraft was designed by Roy Chadwick as the Avro Type 696. It was clearly based on the Avro Lincoln and the successful wartime Avro Lancaster, which was the then current ASW aircraft. Taking the Lincoln's wings and landing gear and mating them with a new fuselage and using Rolls-Royce Griffon engines with 13 feet contra-rotating propellors, creating a distinctive engine noise and adding high-tone deafness to the hazards of the pilots. The first test flight was in March 1949 and front-line aircraft were delivered to Coastal Command in April 1951 and had their operational debut during the Suez Crisis.
The Mk. II was improved with feedback from operations and is considered by aficionados to be the definitive type. The radome was moved from the nose to a ventral position, to improve all-round coverage and minimise the risk of bird-strikes. Both the nose and tail sections were lengthened, the tail planes were redesigned and the weak undercarriage was strengthened.
The Mk. III was another redesign in response to crew complaints. A new tricycle undercarriage was introduced, the fuselage was increased in all main dimensions and had new wings with better ailerons and tip tanks. In a sop to the crews on fifteen hour flights the sound deadening was improved and a proper galley and sleeping space were included. Total take-off weight had risen by over 30,000 lb (Ph. III) and assistance from Rolls-Royce Viper 203 turbojets was needed on take-off. This extra strain told on the airframe and the flight life of the Mk. IIIs was sufficiently reduced that they were out-survived by the Mk. IIs.
All marks suffered from using the Griffon engines - thirsty, noisy and temperamental they were constantly on the cusp of being replaced but even the potentially beneficial Napier Nomad re-engine didn't quite happen.
In ASW the Shackleton carried both types of sonobuoy, ESM, a diesel fume detection system and for a short time an unreliable MAD sytem. Weapons were nine bombs, or three torpedoes or depth-charges, and 20 mm cannon.
The need to replace the Shackleton was first raised in the early 1960s. The arrival of the BAe Nimrod in 1969 was the end for the Shackleton in most roles but it continued as the main SAR aircraft until 1972. The intention to retire the aircraft was then thwarted by the need for AEW converage in the North Sea and northern Atlantic following the retirement of the Fairey Gannet. With a new design not due until the late 1970s the existing AN/APS-20 radar was installed in Mk. IIs as an interim measure, the AEW.2, from 1972. The disastrous Nimrod AEW replacement program dragged on and on and the eventual successor to the Shackleton did not arrive until the RAF finally gave in and purchased the E-3 Sentry in 1991.
A total of 185 Shackletons were built from 1951 to 1958, around twelve are still believed to be intact - with one still flying.