That phalanx gun has a radar that steers a continuous stream of bullets into any fast moving object tracked by the Doppler radar. They can be fully automatic so that there is no need for humans to select targets and approve their removal. Even fast jets are no match. However, like most things designed during the cold war, the design specs forgot about slow things like terrorists in fishing boats or in our case, catamarans. Now they are being retrofitted with optical systems to fix this flaw. The 'new' military now has weapons optimized to take out catamarans :-)

Matt