The attack aircraft as a role was defined by its use during World War I, in support of ground forces on battlefields. Battlefield support is generally divided into close air support and battlefield air interdiction, the first requiring strict and the latter only general cooperation with friendly surface forces. though such aircraft also attacked targets in rear areas. Such missions required flying where light anti-aircraft fire was expected and operating at low altitudes to precisely identify targets. Other roles, including those of light bombers, medium bombers, dive bombers, reconnaissance, fighters, fighter-bombers, could and did perform air strikes on battlefields. All these types could significantly damage ground targets from a low level flight, either by bombing, machine guns, or both.