How high do military aircraft fly?

Military aircraft do not fly at a fixed altitude, but at whatever each mission requires. Transports like the A400M or the C-130, and tankers like the A330 MRTT, use the same airways and flight levels as commercial airliners, between 9,000 and 12,000 m, because fuel burn is lower there. Fighters in transit do the same, and in air-to-air combat they favor the high band, between 9,000 and 12,000 m, where thinner air allows more speed and greater range for launched missiles. The service ceiling of a Eurofighter Typhoon is 16,700 m (55,000 ft) and an F-22's exceeds 19,800 m (65,000 ft), but those are exceptional altitudes, not everyday operating ones.

At the other extreme is low-level flying, practiced to escape radar and long-range missiles. Fighters and helicopters train along published corridors at 75-150 m above the ground (250-500 ft), and in some countries, with special authorization, even lower. It is the type of flight most noticeable from the ground, because of the sudden noise and the high-speed pass, which is why air forces publish the routes and hours of use.

A few aircraft operate above everything else. The Lockheed U-2 reconnaissance aircraft flies above 21,000 m (70,000 ft), where the pilot wears a pressure suit similar to an astronaut's, and the unmanned RQ-4 Global Hawk operates around 18,000 m. Early-warning aircraft like the E-3 patrol at about 9,000 m to cover the widest possible radar horizon for hours at a time. All of their altitudes are measured in feet in day-to-day operations, but technical specifications use both units.