Taken from Wikipedia, reference the Goalkeeper system:
Description
The system first acquires a target using the 2D X-Band search radar, which can track up to 18 targets at once. The engagement radar is then slewed to the heading indicated by the search radar. The engagement radar operates in both
X-Band and
Ka-Band, this enables the engagement radar to use the search radars signal to find the target quickly without additional searching, also data from the X-Band and Ka-Band return signals can be compared to increase resistance to
ECM and clutter. The engagement radar is also backed up by an optical system.
The
GAU-8/A Avenger 30 mm gun, as used by the
A-10 Thunderbolt II was selected for the system, primarily because although the muzzle velocity and range are similar to the
M61 Vulcan the projectiles are much heavier (430 grams compared to 100 grams). This is critical because
supersonic missiles that are damaged may still have enough momentum to hit the ship—the only way to ensure the protection of the ship is either detonate the warhead of the missile or obliterate the missile.
The system's reaction time to a
Mach 2 sea-skimming missile like the Russian
SS-N-22 Sunburn from automatic detection to kill is reported to be 5.5 seconds with the engagement starting at a range of 1500 m and ending with a kill at 300 m.