Goalkeeper is also a CIWS (close-in weapons system) used by the British, Dutch, German and several other nations', navies. It consists of a GAU-8 30mm cannon mounted on a turreted gun director and radar system.
Its operation is very similar to the US-designed Phalanx CIWS system, but it fires larger, more destructive rounds. In addition to killing enemy fighter aircraft and cruise missiles, it is capable of destroying tanks and lightly armored warships.
A single strike from the 30mm does so much more damage than the armor-piercing discarding sabot 20mm (a 12.7mm tungsten slug with an aluminum sabot to allow it to be fired from a 20mm barrel) used by Phalanx that Goalkeeper is considered by many to be a superior defense, especially against armored missiles and heavy attack aircraft.
The use of 30mm ammunition also allows proximity-fused high-explosive fragmentation rounds, which do not require direct hits to destroy targets.