Editing Avro Shackleton (section)

===Further development===
[[File:Avro 696 Shackleton MR.1 VP256 B-A 269 Sqn RWY 24.07.53 edited-2.jpg|thumb|left|Shackleton MR.1 of [[No. 269 Squadron RAF|269 Squadron]] with dorsal turret in 1953]]

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 [[air-to-surface-vessel radar|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.<ref name="World Aircraft Information Files">''World Aircraft Information Files'' 1997.</ref> Both the nose and tail section were lengthened, the [[tailplane]] was redesigned, the undercarriage was strengthened and twin-retractable tailwheels were fitted. The [[Bristol Aeroplane Company|Bristol]] dorsal turret was initially retained, but was later removed from all aircraft after delivery.<ref name="jeff 74-75">Jefford et al. 2005, pp. 74–75.</ref> 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.

[[File:Avro Shackleton MR.2 WG557 T-L 220 Sqn BLA 06.09.55.jpg|thumb|left|Shackleton MR.2 of [[No. 220 Squadron RAF]] in September 1955]]

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.<ref name="World Aircraft Information Files"/> Production of the MR 2 ended in May 1954.<ref name="jones 85">Jones 2002, p. 85.</ref>

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.<ref>Jones 2002, pp. 93, 95–96.</ref> The weapons capability was also upgraded to include homing torpedoes and [[Mk 101 Lulu|Mk 101 Lulu nuclear depth bombs]].<ref name="World Aircraft Information Files"/> To reduce crew fatigue on 15-hour flights, the sound deadening was improved and a proper [[Galley (kitchen)|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&nbsp;lb (13,600&nbsp;kg) (Ph. III) and assistance from [[Armstrong Siddeley Viper]] Mk 203 [[turbojet]]s 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.<ref>The Shackleton, Chris Ashworth, Aston Publications Limited 1990, {{ISBN|0 946627 16 9}}, p.44</ref><ref>[http://www.shackletonproject.co.za/saaf4.html "Shackletons in the SAAF – Retirement."] {{webarchive |url=https://web.archive.org/web/20080223160750/http://www.shackletonproject.co.za/saaf4.html |date=23 February 2008 }}  ''The Shackleton Project''. Retrieved: 10 July 2008.</ref><ref name="jeff 77-78">Jefford et al. 2005, pp. 77–78.</ref> 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.<ref name="jeff 88">Jefford et al. 2005, p. 88.</ref> The Shackleton IV was cancelled in 1955, the Canadian requirement being subsequently met by the ''Britannia Maritime Reconnaissance'', based on the [[Bristol Brittania]] airliner, later entering production as the [[Canadair CP-107 Argus|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.<ref name="jones 84-85">Jones 2002, pp. 84–85.</ref>