Sea Eagle (missile)

The anti-ship version of the Martel missile entered service with the RAF in October 1972 and the Royal Navy one year later. These missiles were designed around a television guidance system using a camera in the nose of the missile that sent its image back to the launch aircraft via a data link radio system. The weapons officer in the aircraft, normally the Blackburn Buccaneer, used the image to guide the missile via signals sent back to the missile on the same data link. This method of operation had been chosen for its simplicity; in comparison, an active radar seeker would be prone to all sorts of countermeasures, including chaff and active jamming systems, and would require some form of navigation system for the approach while the missile was still under the radar horizon.

The desire for a ship-launched anti-ship missile led to some consideration of an active seeker for the Martel, under the name Ship Martel (or Active Martel). As the launching ship would be under the radar horizon of the target, a data link or similar solution that required a line-of-sight would not work. Marconi won the contract for the radar seeker, a very simple one-axis (left-right) seeker that they claimed would be much less expensive than the Adac seeker of Exocet or the RE576 used on the AS.34 Kormoran and Otomat. A small rocket booster would be used to launch the missile before starting the original engine.[1] This role was ultimately filled by the Exocet and development ended.[2]

The Ship Martel work was later picked up for a submarine-launched anti-ship missile, a project known as CL.137 USGW (Under-Sea Guided Weapon).[lower-alpha 1] This consisted of a Sea Martel with modifications to allow it to fit into a normal 21-inch torpedo tube, using folding wings and fins.[4] The Marconi seeker was used, but was not fitted during testing. Instead, a simple autopilot with a radar altimeter was used in testing at Aberporth.[1] A further adaptation was the Sub Martel, otherwise similar but using the Adac seeker from the Exocet, a sub-launched development of the Exocet itself having been abandoned for cost reasons.[4] Ultimately the USGW contest was won by the Sub-Harpoon in September 1975.[5]

Sea Eagle on the right, next to a Martel in the center. The similarity of the designs is evident. The weapon on the left is a WE177A.

These developments all suggested the TV-guided Martel was no longer competitive, and a series of studies during 1973 to 1975 came up with specifications for its replacement. This was known as Air Staff Target (AST) 1226 in the Air Force, and Naval Staff Target (NST) 6451 in the Navy. This called for a missile with greater range than Ship Martel, which required the switch to a jet engine. Hawker Siddeley submitted a design using the Marconi seeker and a more highly modified version of the Martel airframe. This would have the advantage of being able to be fired from any aircraft already able to fire the TV-guided Martel.[5]

Design of the P3T began in 1976, with full scale development initiated in 1979. Although the resulting design looked like the Martel, almost all components differ, with a longer body, larger wings and totally different internal components. A ship-launched version, the P5T Sea Eagle SL, was proposed in 1981. This added two solid-fuel boosters on either side of the missile body, but was otherwise similar to the P3T. It was designed to be fired from its sealed shipping box. The same box was used for the proposed Lightweight Sea Dart, allowing a ship to carry either or both on the same launcher. One advantage to the SL version over competing designs was that it could be fired at very close targets, while most designs, like Harpoon and Exocet, had a fairly long minimum range.[6] Another advantage was that the same missile could be fired from helicopters, like the original Martel, as the rockets could launch it from the helicopter even at very low altitudes without needing high forward speed to allow the small wings to maintain altitude.[7]

Production of the finished production weapon began in 1982, around the same time that the name Sea Eagle was bestowed, with test firings up to 1984 and service introduction the following year. The RAF Buccaneer was the first aircraft to carry a Sea Eagle in active service. This was followed by the Royal Navy's Sea Harrier, as well as the Tornado GR1B in the RAF (replacing Buccaneers) and Royal Saudi Air Force. The Indian Navy also equipped its Sea Harrier FRS Mk.51 and Jaguar IM with the missile, as well as twenty Sea King Mk.42B helicopters, using a version with two booster rockets either side of the rear fuselage. Indian Ilyushin Il-38 maritime patrol aircraft were also equipped with the rocket-boosted version of the missile, carried on unusual side-fuselage pylons aft of each wing. It has also been reported that India sought to equip its Tupolev Tu-142 fleet with the missile. The Chilean Air Force has trial fitted its A-36M Halcon (CASA 101 Aviojet) with the missile, but this combination never entered service. Several variants of the BAE Hawk trainer/light fighter have carried the missile on trials.

The Sea Eagle was withdrawn from service with the RAF and Royal Navy by 2000.[8]