Aerial warfare is the use of military aircraft and other flying machines in warfare. Aerial warfare includes bombers attacking enemy concentrations or strategic targets; fighter aircraft battling for control of airspace; attack aircraft engaging in close air support against ground targets; naval aviation flying against sea and nearby land targets; gliders, helicopters and other aircraft to carry airborne forces such as paratroopers; aerial refueling tankers to extend operation time or range; and military transport aircraft to move cargo and personnel. Historically, military aircraft have included lighter-than-air balloons carrying artillery observers; lighter-than-air airships for bombing cities; various sorts of reconnaissance, surveillance and early warning aircraft carrying observers, cameras and radar equipment; torpedo bombers to attack enemy shipping; and military air-sea rescue aircraft for saving downed airmen. Modern aerial warfare includes missiles and unmanned aerial vehicles. Surface forces are likely to respond to enemy air activity with anti-aircraft warfare.