Avro Shackleton

The Avro Shackleton was a British long-range maritime patrol aircraft used by the Royal Air Force (RAF) and the South African Air Force (SAAF). It was developed by Avro from the Avro Lincoln bomber, itself being a development of the famous wartime Avro Lancaster bomber. It was replaced by Nimrod maritime patrol aircraft in the 1970s. The aircraft was also adapted for airborne early warning (AEW) roles within the RAF, replaced by the Boeing E-3 Sentry in 1990. The type is named after the polar explorer Sir Ernest Shackleton.

Entering service with the RAF in 1951, the Shackleton was used primarily in the anti-submarine warfare (ASW) and maritime patrol aircraft (MPA) roles; it also became used as a search and rescue (SAR) platform and for performing several other secondary roles such as being a troop-transport. In later life, a small number of the RAF's Shackletons were subsequently adapted for airborne early warning (AEW) duties, performing in this capacity until the type's retirement in 1991. The Shackleton was also procured by South Africa, and was operated by the SAAF between 1957 and 1984.

Avro Shackleton
Class Aircraft
Type Utility
Manufacturer Avro
Origin United Kingdom - UK (Great Britain)
Country Name Origin Year
United Kingdom - UK (Great Britain) 1949
Country Name Operational Year Retirement Year
South Africa View
United Kingdom - UK (Great Britain) 1951 1991 View
ManufacturerName Production From Production To Quantity
Avro 185 View

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, in particular the elimination of oxygen restrictions that had previously limited underwater endurance via the use of a snorkel to eliminate the need for surfacing when recharging a vessel's batteries. 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 as Maritime Reconnaissance Mk 3 (MR3) - as a stop-gap measure for maritime search and rescue and general reconnaissance duties; however, RAF Coastal Command had diminished to only a third of its size immediately prior to the Second World War.

In the emerging climate of the Cold War and the potential 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 for 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 general reconnaissance and air/sea rescue aircraft; they formalised 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 upon the Lincoln. Elements of the Avro Tudor airliner were also reused in the design; Lincoln and Tudor had been derivatives of the successful wartime Avro Lancaster bomber. Crucially, the new aircraft was to be capable of a 3,000 nautical mile range while carrying up to 6,000 lb of weapons and equipment. In addition to featuring a large amount of electronic equipment, the Type 696 had a much improved crew environment over other aircraft types to allow them to be more effective during the lengthy mission times anticipated. At one stage during development, the Type 696 was referred to as the Lincoln ASR.3 before this was discarded in favour of the Shackleton name.

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 re-designated "Maritime Reconnaissance Mark I" (MR 1). The prototype differed from subsequent production Shackletons in a number of areas; it featured a number of turrets and was equipped for air-to-air refuelling using the looped-line method. These did not feature on production aircraft due to judgments of ineffectiveness or performance difficulties incurred. However, the performance of the prototype had been such that, in addition to the go-ahead for the MR1's production, a specification for 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.

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 only be fully extended with the bomb bay doors open. It had improved all-round radar coverage and minimised the risk of bird-strikes. Both the nose and tail section were lengthened, the tailplane was redesigned, the undercarriage was strengthened and twin-retractable tail wheels were fitted. The dorsal turret was initially retained, but was later removed from all aircraft after delivery. The prototype, VW 126, was modified as an aerodynamic prototype at the end of 1950 and first flew with the MR 2 modification on 19 July 1951.

VW 126 was tested at Boscombe Down in August 1951, particular attention was paid to changes made to improve its ground handling, like the addition of toe-brakes 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 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.

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. The weapons capability was also upgraded to include homing torpedoes and Mk 101 Lulu nuclear depth bombs. To facilitate crews on 15-hour flights, the sound deadening was improved and a proper galley and sleeping space were included. Due to these upgrades, the take-off 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 take-off (JATO). This 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 a practically 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. The Shackleton IV was cancelled in 1955.

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.

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 outer wings; at one stage during development, the tail plane had closely resembled the Lincoln's, but were 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. Later variants of the Shackleton were substantially redesigned, adopting a new nose-wheel undercarriage, redesigned wings and centre-section, and a larger fuel capacity for more range.

Variants

Avro 696 Shackleton prototypes

Three prototype Type 696s were ordered in May 1947 to meet specification R 5/46:

  • VW126
  • VW131
  • VW135

Avro 696 Shackleton Mk.1

  • Shackleton MR.Mk.1
  • Shackleton MR.Mk.1A
  • Shackleton T.4

Avro 696 Shackleton Mk.2

Shackleton MR.Mk.2

  •     Shackleton MR.Mk.2 Phase 1 or MR.Mk.2C
  •     Shackleton MR.Mk.2 Phase 2
  •     Shackleton MR.Mk.2 Phase 3

Shackleton T.2  

Shackleton AEW.2

Avro 716 Shackleton Mk.3

Shackleton MR.Mk.3

    The aircraft underwent several phased modifications:

  •     Shackleton MR.Mk.3 Phase 1
  •     Shackleton MR.Mk.3 Phase 2
  •     Shackleton MR.Mk.3 Phase 3

Projected designs

  • Avro 717 and 719 Shackleton MR.Mk.4
  • Shackleton MR.Mk.5



Royal Air Force

On 30 March 1951, the first Shackleton was delivered to No. 120 Squadron RAF; by the end of 1952 seven squadrons were operating the type. The first operational deployment of the Shackleton occurred in 1955 as a troop-transport for British Army movements to Cyprus; less than a year later, the type's first combat deployment took place during the Suez Crisis, codenamed Operation Musketeer.

During the 1960s, the typical Shackleton crew comprised two pilots, two navigators, a flight engineer, an air electronics officer, and four air electronics operators. During this period, equipment upgrades has become routine in order to keep pace with ever more capable submarines; problems with airframe fatigue were identified, leading to several programs being carried out 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.

Maritime reconnaissance was a large element of the Shackleton's service. This mission was often performed to identify and monitor naval and merchant shipping and to demonstrate sovereignty. During the Indonesia–Malaysia confrontation in the 1960s, Shackletons monitored the seas for vessels involved in arms smuggling. Similar operations were conducted in Cyprus, and Shackletons operating from bases in Madagascar cooperated with Royal Navy vessels to enforce a United Nation-mandated oil blockade of Rhodesia.

The Shackleton would often be used in to perform search and rescue missions, at all times one crew was kept on standby somewhere across the UK for this role. The Shackleton had also replaced the Avro Lincoln in the colonial policing mission, aircraft would often be stationed in the Aden Protectorate and Oman 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. Other roles included weather reconnaissance and transport duties, in the latter role each Shackleton could carry freight panniers in the bomb bay or up to 16 fully equipped soldiers.

In 1969, a jet-powered replacement patrol aircraft, the Hawker Siddeley Nimrod, began to enter RAF service, which was to spell the end for the Shackleton in most roles. While radically differing in external appearance, the Shackleton and the initial version of the Nimrod shared many sensor systems and onboard equipment.

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 the Fleet Air Arm's Fairey Gannet aircraft used in the AEW role in the 1970s. As an interim replacement, the existing AN/APS-20 radar was installed in modified Shackleton MR 2s, redesignated the AEW 2, as an interim measure from 1972. These were operated by No. 8 Sqn, based at RAF Lossiemouth. All 12 AEW aircraft were given names from The Magic Roundabout and The Herbs TV series. The intended replacement, the British Aerospace Nimrod AEW3, suffered considerable development difficulties which culminated in the Nimrod AEW 3 being cancelled in favor of an off-the-shelf purchasing of the Boeing E-3 Sentry, which allowed the last Shackletons to be retired in 1991.

South African Air Force

During the Second World War, the importance of securing the sea routes around the Cape 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. In the post-war situation, the South 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 aging Short Sunderland maritime patrol aircraft. Modifications were required to fulfill South African conditions and requirements, such as the ability to operate over the Indian Ocean, the resulting aircraft was designated as the Shackleton MR 3.

On 18 August 1957, the first two Shackletons were delivered to D.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 by 35 Squadron SAAF. The type typically patrolled the sea lanes around the Cape of Good Hope, often monitoring Soviet vessels traversing between the Indian and Atlantic oceans. The Shackleton was briefly used in low-level overland patrols along the Southern Rhodesian border, but these duties ended following concerns of the disturbance of wildlife.

Often, the Shackleton would be called in to perform search and rescue operations in the treacherous waters around the Cape. In March 1971, Shackletons successfully intervened in the SS Wafra oil spill, deliberately sinking the stricken oil tanker with depth charges in order to prevent an ecological disaster. 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 13 crew.

Due to an embargo imposed by the United Nations over South Africa's policy of apartheid, acquiring components for the Shackleton fleet became increasingly difficult and thus the aircraft's serviceability suffered. The fleet had been modified to Phase III standards prior to the implementation of the arms embargo, albeit without the auxiliary Viper engine. 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. Although the joke has been applied to several aircraft, the Shackleton was often described as "a hundred thousand rivets flying in close formation." 

Role Maritime patrol aircraft
Manufacturer Avro
First flight 9 March 1949
Introduction April 1951
Retired 1991
Primary users Royal Air Force
South African Air Force
Produced 1951–1958
Number built 185
Developed from Avro Lincoln


General characteristics

  • Crew: 10
  • Length: 87 ft 4 in (26.61 m)
  • Wingspan: 120 ft (36.58 m)
  • Height: 17 ft 6 in (5.33 m)
  • Wing area: 1,421 ft (132 m)
  • Airfoil: modified NACA 23018 at root, NACA 23012 at wingtip
  • Empty weight: 51,400 lb (23,300 kg)
  • Max takeoff weight: 86,000 lb (39,000 kg)
  • Fuel capacity: 4,258 imperial gallons (19,360 L))
  • Powerplant: 4 x Rolls-Royce Griffon 57 liquid-cooled V12 engine, 1,960 hp (1,460 kW) each

Performance

  • Maximum speed: 260 knots (300 mph, 480 km/h)
  • Range: 1,950 nm (2,250 mi, 3,620 km)
  • Endurance: 14.6 hr
  • Service ceiling 20,200 ft (6,200 m)
  • Max wing loading: 61 lb/ft (300 kg/m)
  • Minimum power/mass: 91 hp/lb (150 W/kg)

Armament

  • Twin 20 mm Hispano cannon in the nose; bombs, torpedoes and depth charges as required.

End notes