| Shackleton | |
|---|---|
 Avro Shackleton MR3, in 1955 | |
| General information | |
| Type | Maritime patrol aircraft |
| National origin | United Kingdom |
| Manufacturer | Avro |
| Primary users | Royal Air Force |
| Number built | 185 |
| History | |
| Manufactured | 1951–1958 |
| Introduction date | April 1951 |
| First flight | 9 March 1949 |
| Retired | 1991 |
| Developed from | Avro Lincoln |
TheAvro Shackleton is a British long-rangemaritime patrol aircraft (MPA) which was used by theRoyal Air Force (RAF) and theSouth African Air Force (SAAF). It was developed byAvro from theirLincolnbomber, which itself had been a development of the famous wartimeLancaster bomber.
The Shackleton was developed during the late 1940s as part of Britain's military response to the rapid expansion of theSoviet Navy, in particular its submarine force. Produced as the primary type equippingRAF Coastal Command, theType 696 as it was initially designated, incorporated major elements of the Lincoln, as well as theAvro Tudor airliner, and was furnished with an extensive electronics suite in order to perform theanti-submarine warfare (ASW) mission, along with much-improved crew facilities due to the long mission times involved in patrol work. The type was namedShackleton, after the polar explorer SirErnest Shackleton.[N 1]
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 aerialsearch 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 theSSWafra oil spill, intentionally sinking the stricken oil tanker usingdepth charges to prevent further ecological contamination.
During the 1970s, the Shackleton was replaced in the maritime patrol role by thejet-poweredHawker Siddeley Nimrod, however a small number of the RAF's existing Shackletons received extensive modifications in order to adapt them to perform theairborne early warning (AEW) role. The type continued to be used in this role until 1991, when it was replaced by theBoeing E-3 Sentry AEW aircraft. These were the last examples of the type remaining in active service.
TheBattle of the Atlantic was a crucial element of theSecond World War, in which Britain sought to protect its shipping from the GermanU-boat threat. The development of increasingly capablediesel-electric submarines had been rapid, and in particular thesnorkel 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.[3] In addition,lend-leased aircraft such as theConsolidated B-24 Liberator had been returned following the end of hostilities. SeveralAvro Lancasters had undergone rapid conversion (designated Maritime Reconnaissance Mk 3 (MR3)) as a stopgap measure for maritime search and rescue and general reconnaissance duties;[4] however,RAF Coastal Command had diminished to only a third of its size immediately after the Second World War.[5]
In the emerging climate of theCold War, and the requirement to guard the North Atlantic from an anticipated rapid expansion of theSoviet Navy's submarine force, a new aerial platform to perform the anti-submarine mission was required.[5][6] 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 forFar 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 theAvro Lincoln as a general reconnaissance and air/sea rescue aircraft, formalising their requirements for such an aircraft underAir Ministry specification R.5/46. Avro's Chief DesignerRoy Chadwick initially led the effort to build an aircraft to this requirement, designated as the AvroType 696.[2][7]
The Type 696 was a significant development of the Lincoln. Elements of theAvro Tudor airliner were also reused in the design, both the Lincoln and the Tudor being derivatives of the successful wartimeLancaster bomber.[8][9] 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.[10][11] During development the Type 696 was provisionally referred to as theLincoln ASR.3 before the official name 'Shackleton' was selected.
The first test flight of the prototype Shackleton GR.1,serialVW135, was made on 9 March 1949 from the manufacturer's airfield atWoodford, Cheshire in the hands of Avro's Chief Test Pilot J.H. "Jimmy" Orrell.[12] 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 severalgun turrets and was equipped for air-to-air refuelling using thelooped-line method. These did not feature on production aircraft due to performance difficulties or being judged ineffective.[13] 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.[14] By 1951, the MR1 had become officially considered as an interim type due to several shortcomings.[15]
TheMR 2 was an improved version of the Shackleton, featuring numerous refinements that had been proposed for the MR1. The radar was upgraded toASV Mk 13, and theradome relocated from the aircraft's nose to aventral 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.[16] Both the nose and tail section were lengthened, thetailplane was redesigned, the undercarriage was strengthened and twin-retractable tailwheels were fitted. TheBristol dorsal turret was initially retained, but was later removed from all aircraft after delivery.[17] 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.[16] Production of the MR 2 ended in May 1954.[18]
TheType 716 ShackletonMR 3 was another redesign in response to crew feedback and observations. A newtricycle undercarriage was introduced, the fuselage was increased in all main dimensions and had new wings with better ailerons and tip tanks.[19] The weapons capability was also upgraded to include homing torpedoes andMk 101 Lulu nuclear depth bombs.[16] To reduce crew fatigue on 15-hour flights, the sound deadening was improved and a propergalley 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 fromArmstrong Siddeley Viper Mk 203turbojets 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.[20][21][22] 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.
TheType 719 Shackleton IV, later known as theMR 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 theNapier Nomad compound engine.[23] The Shackleton IV was cancelled in 1955, the Canadian requirement being subsequently met by theBritannia Maritime Reconnaissance, based on theBristol Brittania airliner, later entering production as theCanadair 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.[24]
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.[2] 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.[25][26] 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.[27]
Various armaments and equipment were carried by the Shackleton in order to perform its missions. In ASW operations, theASV Mk 13 radar was the primary detection tool. It could detect a destroyer at a range of 40 nautical miles (46 mi; 74 km), a surfaced submarine at 20 nautical miles (23 mi; 37 km), and a submarine'sconning tower at 8 nautical miles (9.2 mi; 15 km), although rough seas considerably reduced the radar's effectiveness.[28][29] Other equipment included droppablesonobuoys,electronic warfare support measures and anAutolycus 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.[30] Weapons carried included up to nine bombs, three homingtorpedoes ordepth-charges. The aircraft also had two20 mm cannon in a Bristol dorsal turret. Anin-flight refueling receptacle could be accommodated, but was not fitted on production aircraft.[28]
The Merlin engines were replaced with the larger, more powerful and slower-revvingRolls-Royce Griffons with 13-foot-diameter (4.0 m)contra-rotating propellers. This engine's distinctive noise often caused crew members to develop high-tone deafness. The Griffon was needed because the Shackleton was heavier and had more drag than the Lincoln.[31][32] The Griffon provided equivalent power to the Merlin but at lowerengine speed, which led to reduced fuel consumption in the denser air at low altitudes; the Shackleton would often loiter for several hours at roughly 500 ft (150 m) or lower when searching for submarines. Lower-revving Griffons, compared to Merlins, reduced engine stress which improved their reliability. Using conventional propellers would have needed an increase in propeller diameter to absorb the engine's power andtorque, but this was not possible due to space limitations imposed by the undercarriage length and enginenacelle positioning, so the contra-rotating propellers were adopted, which gave greater blade area within the same propeller diameter.
Numerous problems were encountered during the Shackleton's operational service. In practice, the diesel fume detection system was prone to false alarms and thus received little operational use. The engines, hydraulics and elements of the avionics were known for their unreliability, and the aircraft proved to be fairly maintenance-intensive. The prototype MR 3 was lost due to poor stalling characteristics. This was rectified prior to production, although a satisfactory stall-warning device was not installed until 1969. The Shackleton is often incorrectly assigned the unfortunate distinction of holding the record for the highest number of aircrew killed in one type in peacetime in the RAF.[33] However the true figures suggest that some of its contemporaries fared far worse, for example the Gloster Meteor with over 430 fatalities[34] against the Shackleton's 156. Several programs to support and extend the fatigue life of the Shackleton's airframe were required; the fatigue life problems ultimately necessitated the rapid introduction of a whole new maritime patrol aircraft in the form of theHawker Siddeley Nimrod, which began being introduced to RAF service in 1969.[35]
On 30 March 1951, the first Shackleton was delivered toNo. 120 Squadron RAF; by the end of 1952 seven squadrons were operating the type,[36] which soon came to be nicknamedThe Growler on account of the engine noise from the four Rolls-Royce Griffon engines.[37] The first operational deployment of the Shackleton occurred in 1955 as a troop-transport forBritish Army movements toCyprus. Less than a year later, the type's first combat deployment took place during theSuez Crisis, codenamedOperation Musketeer.[38]
In 1957, British RAF Shackletons participated heavily during theJebel Akhdar War inOman to expand the territory of the Sultanate, which was ade facto British colony,[39][40][41] in order to gain access to oil wells in the interior of the country. The RAF made 1,635 raids, dropping 1,094 tons of bombs and firing 900 rockets at the interior of Oman between July and December 1958, targeting insurgents, mountain top villages, water channels and crops in a war that nevertheless remained low profile.[40][42][43]
During the 1960s, the typical Shackleton crew comprised two pilots, two navigators, a flight engineer, an air electronics officer, and four air electronics operators.[44] During this period, equipment upgrades had become routine in order to keep pace with ever more capable submarines. Problems with airframe fatigue were identified, leading to several programmes to strengthen the aircraft and thus extend its viable service life. In 1966,nuclear depth charges were introduced to the Shackleton's arsenal with the aim of countering the Soviets' development of deep-diving submarines.[45]
Maritime reconnaissance was a large element of the Shackleton's service, this mission being to identify and monitor naval and merchant shipping, and to demonstrate sovereignty. During theIndonesia–Malaysia confrontation in the 1960s, Shackletons monitored the seas for vessels involved inarms smuggling. Similar operations were conducted inCyprus, and Shackletons operating from bases inMadagascar co-operated withRoyal Navy vessels to enforce aUnited Nations-mandated oil blockade ofRhodesia.[46]
The Shackleton would often be used to performsearch and rescue missions, one crew and aircraft being kept on standby somewhere in the UK for this role. The Shackleton also replaced the Avro Lincoln in the colonial policing mission, aircraft often being stationed in theAden Protectorate andOman to carry out various support missions, including convoy escorting, supply dropping, photo reconnaissance, communication relaying, and ground-attack missions. The Shackleton was also employed in several short-term bombing operations.[47] Other roles included weather reconnaissance and transport duties, in the latter role each Shackleton carrying freight panniers in the bomb bay or up to 16 fully equipped soldiers.[48]
In 1969, a jet-powered replacement patrol aircraft, theHawker Siddeley Nimrod, began to enter RAF service, which was to spell the end for the Shackleton in most roles. While radically different in external appearance, the initial version of the Nimrod shared many sensor systems and onboard equipment with the Shackleton.[49]
The intention to retire the Shackleton was thwarted by the need to provide AEW coverage in the North Sea and northern Atlantic following the withdrawal of theFleet Air Arm'sFairey Gannet aircraft used in the AEW role in the 1970s. As an interim replacement, the existingAN/APS-20 radar from the Gannets was installed in modified Shackleton MR 2s, redesignatedAEW 2, from 1972. These were operated byNo. 8 Sqn, based atRAF Lossiemouth. All 12 AEW aircraft were given names fromThe Magic Roundabout andThe Herbs TV series.[16] The intended replacement, theBritish Aerospace Nimrod AEW3, suffered considerable development difficulties which culminated in it being cancelled in favour of an off-the-shelf purchase of theBoeing E-3 Sentry, finally allowing the last Shackletons to be retired in 1991.[50]
During the Second World War, the importance of securing the sea routes around theCape of Good Hope had been made apparent, with over a hundred vessels being sunk in South African waters by enemy vessels between 1942 and 1945.[51] Postwar, theSouth African Air Force sought a large and capable platform to perform the maritime patrol role. After evaluating four RAF MR 2s in 1953, an order was placed for eight Shackletons as a replacement for the SAAF's agingShort Sunderland maritime patrol aircraft. Modifications were required to match South African conditions and requirements, such as the ability to operate over theIndian Ocean. The resulting aircraft was designated the Shackleton MR 3.[27][52]
On 18 August 1957, the first two Shackletons were delivered toD.F. Malan Airport,Cape Town. Two more followed on 13 October 1957 and the remainder arrived in February 1958. Delivered to the same basic standard as the RAF's MR 3s, they were assigned single letter codes between "J" and "Q" and operated by35 Squadron SAAF. The type typically patrolled the sea lanes around the Cape of Good Hope, often monitoring Soviet vessels transiting between the Indian and Atlantic oceans. The Shackleton was briefly used in low-level overland patrols along theSouthern Rhodesian border, but these duties ended following concerns of the disturbance of wildlife.[51][53]
The Shackleton would often be called upon to perform search and rescue operations in the treacherous waters around the Cape. In March 1971, Shackletons successfully intervened in theSS Wafra oil spill, deliberately sinking the stricken oil tanker with depth charges in order to prevent an ecological disaster.[54] The only operational loss incurred was 1718 K, which crashed into the Wemmershoek mountains at night time on 8 August 1963 with the loss of all thirteen crew.[51]
South Africa's policy ofapartheid led to anembargo imposed by theUnited Nations, which made acquiring components for the Shackleton fleet increasingly difficult, the aircraft's serviceability suffering as a result.[51] The fleet had been modified to Phase III standards prior to the implementation of the arms embargo, albeit without the auxiliary Viper engine.[54] Two of the aircraft were re-sparred, 1716 J in the United Kingdom and 1717 O in South Africa by the SAAF, but the lack of engine spares and tyres, together with airframe fatigue, took a gradual toll. By November 1984, the fatigue lives of all but the two re-sparred aircraft had expired and the fleet was retired into storage.[16] Although the joke has been applied to several aircraft, the Shackleton was often described as "a hundred thousand rivets flying in close formation."[55][56]
Three prototype Type 696s were ordered in May 1947 to meet specification R 5/46:
The Mark 2 had a longer nose and the radome was moved to the ventral position. A lookout position was added to the tail, two more 20 mm cannons were added in the nose, and twin retractable tailwheels were fitted. One aircraft, WB833, originally ordered as an MR.1 was built as an MR.2 prototype and first flew on 17 June 1952.[58] The last ten MR.1s on the production line were completed as MR.2s and orders for 80 new-build aircraft were placed; the last 21 were completed as MR.3s, the total number of MR.2s built being 69.[59] The first aircraft entered service with42 Squadron atRAF St Eval in January 1953.[59]
Mk.2s were later modified in parallel with phased modifications to the Mk.3:[60]
MR.Mk.2 Phase 1 or MR.Mk.2C: as per Mk.3 Phase 1.[58] Also received the sonics plotting table from the Mk.3.
MR.Mk.2 Phase 2: as per Mk.3 Phase 2.[58]
MR.Mk.2 Phase 3: as per Mk.3 Phase 3, except that the Viper engines were not fitted.[58]
Shackleton T.2Ten MR 2 Phase 3 aircraft were modified in 1967 as T.2s at Langar to replace the T.4s with the Maritime Operational Training Units as radar trainers, with master and slave radar positions for training installed.[58]
Shackleton AEW.2In 1971 twelve MR.2s were converted at Woodford and Bitteswell as Airborne Early Warning aircraft, being fitted withAN/APS-20 radar in order to perform theAirborne Early Warning role. The first AEW.2 flew on 30 September 1971 and the type entered service with8 Squadron on 1 January 1972.[58] The AEW.2 was retired on 1 July 1991.[61]
Shackleton MR.Mk.3Tailwheel undercarriage replaced by a tricycle undercarriage, nose entrance hatch added and wingtip tanks fitted to increase fuel capacity.[59] To increase crew comfort the inside was sound proofed, better crew seats were fitted and the tactical team positions rearranged.[59] To make room for some of the internal rearrangement the dorsal turret was deleted.[59] The first MR.3 flew on 2 September 1955; the aircraft had problems with stalling characteristics and crashed on 7 December 1956.[59] The variant entered service with 220 Squadron at RAF St Eval in August 1957.[59] The RAF ordered 52 aircraft but later, following the 1956 Defence Review, the order was reduced to 33 aircraft.[59] An additional aircraft was also built to replace the aircraft lost during stalling trials.[59] An additional eight aircraft were exported toSouth Africa.
The aircraft underwent several phased modifications:
The Phase 1 update introduced changes mainly to the internal equipment.[59]
The Phase 2 update introducedECM equipment, the distinctiveOrange Harvest 'spark plug'ESM aerial and an improved High Frequency radio.[59]
The Phase 3 update introduced twoArmstrong Siddeley Viper turbojet engines at the rear of the outboard engine nacelles to be used for assisted takeoff. The wing main spars had to be strengthened due to the additional engines. A new navigation system was also fitted and there were some modification to the internal arrangement, including a shorter crew rest area to give more room for the tactical positions.[59][62]
A complete list is available here.[77]
| External videos | |
|---|---|
 1990s documentary on the Avro Shackleton | |
| Engine run of a preserved Shackleton | |
| Shackleton displaying at RAF Cosford, 1991 |
Data from Flight International,[90] Jones[91]
General characteristics
Performance
Armament
Avionics
Related development
Aircraft of comparable role, configuration, and era
Related lists
| National | |
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| Other | |
