The Oerlikon 30 mm twin cannon is an

anti aircraft Anti-aircraft warfare, counter-air or air defence forces is the battlespace response to aerial warfare, defined by NATO as "all measures designed to nullify or reduce the effectiveness of hostile air action".AAP-6 It includes surface based, ...

gun, incorporating two

Oerlikon KCB The KCB is a 30 mm caliber autocannon, developed by Hispano-Suiza as HS.831. When Rheinmetall Air Defence, Oerlikon purchased Hispano's armaments division, the gun became KCB. Development HS.831 is a scaled-up version of the 20 mm Hispano-Suiza ...

, used by the

Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...

. They were fitted to Type 42

destroyer In naval terminology, a destroyer is a fast, manoeuvrable, long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against powerful short range attackers. They were originally developed in ...

s after the

Falklands War The Falklands War ( es, link=no, Guerra de las Malvinas) was a ten-week undeclared war between Argentina and the United Kingdom in 1982 over two British dependent territories in the South Atlantic: the Falkland Islands and its territorial de ...

to improve defence against air attack.

References

Naval anti-aircraft guns 30 mm artillery {{UK-navy-stub