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By Mark Hewish
Seawolf has been developed by the British Aircraft Corporation’s Guided Weapons Division to meet the Royal Navy’s requirement for a point- defense missile to arm ships of more than 2,000 tons. It is designed to intercept aircraft, sea-skimming missiles, and small, Mach 2 air-launched, stand-off weapons in severe weather and sea conditions. Firing trials of production-standard rounds are taking place from the Leander-class frigate HMS Penelope. The first ship to carry the weapon operationally will be the “Type 22”-class frigate HMS Broadsword, which is due for completion in late 1978. The last ten Leanders are also scheduled to be armed with Seawolf, and the “Type 21” frigates may additionally be fitted with the missile.
The complete weapon system is designated GWS25. It comprises surveillance radars, trackers using radar and television equipment, launchers, computers, and the associated control equipment. The surveillance radars are Marconi Radar Systems Type 967 for air surveillance and Type 968 for sea search, installed back-to-back in a single housing on a fully-stabilized mounting. Identification friend or foe (IFF) equipment is fitted to the Type
967.
The surveillance radars and IFF detect and identify hostile targets. A Ferranti FM 1600B digital computer automatically allocates threat priorities to targets and a Marconi Radar Systems Type 910 tracker is assigned to the most important objective. The computer instructs the tracker and launcher to turn to the target bearing, and the radar tracker then automatically searches in elevation for the enemy aircraft or missile and locks on to it. The launcher is elevated or depressed to the desired launch angle, and the first missile can then be fired.
The manually loaded launcher contains six rounds in individual cells with double doors at the front and tear. Each missile is treated as a round of ammunition which can remain ready for firing in its cell for 15 months. The weapon is approximately 6.5 feet long and eight inches in diameter; it will fit in the launcher with its wings extended. Seawolf’s Bristol Aerojet Blackcap solid-propellent rocket motor burns for two to three seconds and accelerates the 180-lb. missile to speeds in excess of Mach 2.
Immediately after launch the missile is acquired by the tracking radar’s wide-angle aerial and directed on to the sightline. Steering commands are transmitted to the round by a circular dish mounted on the tracker. Two of these dishes are fitted, allowing a pair of Seawolfs to be fired in salvo against a difficult target. The weapons receive the signals via two aerials mounted in the trailing edges of one pair of wings; the other pair of wings carries radar beacons to aid tracking.
Once the missile has been acquired, the radar tracks both it and the target simultaneously. A guidance shaping unit, based on another FM 1600B computer, generates continuous steering commands to keep the missile on the exact line of sight to the target. If the radar has difficulty in tracking a target at extremely low level, the task can be taken over by a television camera boresighted to the radar aerial. A controller below decks steers the camera, by means of a joystick, so that it follows the target. The television optics are split, allowing the missile to be tracked automatically by means of flares at its rear. Steering commands are sent in the normal way, keeping the missile on the sightline to the target as set up and maintained by the controller. Manual TV tracking is the only aspect of Seawolf operation needing a man in the loop.
The fragmentation warhead, weighing approximately 30 pounds, is detonated by impact or a proximity fuze. Maximum range of the weapon is 2.5 nautical miles,and kill probability is reported to be greater than 80%. (This percentage obviously improves if a salvo is fired.) More than 60 guided missiles have been fired, with the overall success rate reported to be 85%. Targets have included Jindivik drones, 4.5-in. shells, Rushton towed targets, and a Petrel rocket traveling at Mach 2. Seawolf is the West’s only proven antimissile missile.
A loaded Seawolf launcher weighs about 10,000 pounds, and the complete system, including 24 reload rounds in the ship’s magazine, weighs some 55,000 pounds. Lighter and less expensive versions are also being offered by the major contractors. These include the visual-only Seawolf Omega, and the darkfire (target invisible) Seawolf Delta, in which Marconi 800 Series radars replace the Type 910. A further variant is Seawolf Psi, in which the specialized surveillance radars are replaced by existing equipment. Lightweight twin-barreled and triple launchers, which can be elevated to the vertical for rapid reloading by hoist from below decks, replace the six-cell type used in the full system. This allows some launchers to be reloaded while others carry out interceptions, and provides a better defense against stream attacks.