Sea Cat was a British short-range surface to air missile system intended to replace the ubiquitous Bofors 40 mm gun aboard warships of all sizes. It was the world's first operational shipboard point-defence missile system and was designed so that the Bofors guns could be replaced with minimum modification to the recipient vessel using (originally) existing fire-control systems. A mobile land-based version of the system was known as Tigercat.
It was intended to replace the twin 40 mm Bofors Mark V gun and its associated fire-control systems. The original director was based on the STD (Simple Tachymetric Director) and was entirely visual in operation. The target was acquired visually with the missile being guided, via a radio link, by the operator inputting commands on a joystick. Flares on the missile's tail fins aided identifying the missile. The more advanced CRBF (Close Range Blind Fire) director equipped with spin-scanning radar Type 262 for automatic target tracking could also be used.
GWS-20 was trialled on board the Daring class destroyer, and was subsequently removed. It was carried in active service by, (amongst others) Fearless class landing ships and Type 81 Tribal, updated Type 12 Whitby, Type 12I Rothesay and (originally) County class escorts. It was originally intended that all C class destroyers should receive it and the class were prepared accordingly. In the event only HMS Cavalier and HMS Caprice received it, in 1966 refits.
GWS-20 saw active service in the Falklands war onboard the Fearless class and the Rothesay frigates HMS Plymouth and HMS Yarmouth, who retained the GWS-20 director when upgraded to GWS-22.

Despite being obsolete, Sea Cat was still widely fielded by the Royal Navy during the Falklands war. Indeed, it was the sole anti-aircraft defence of many ships. However, unlike the modern and more complex Sea Dart and Sea Wolf systems, Sea Cat rarely misfired or refused to respond, in even the harshest conditions. It was capable of sustained action which compensated for its lack of speed, range, and accuracy, and more importantly, it was available in large numbers. Ships firing Sea Cat made claims on only one confirmed "kill" of Argentine aircraft an A-4C Skyhawk of FAA Grupo 4 on 25 May (the pilot, Lt Lucero ejected) from over 80 launches.