Class A airfield

Class A airfields were World War II military installations constructed to specifications laid down by the British Air Ministry Directorate-General of Works (AMDGW). Intended for use by heavy bombers and transports, they were the standard air base design for the Royal Air Force as well as U.S. Army Air Forces units operating from the British Isles.

Upon the entry of the US into the war a number of RAF Class A bases were transferred to the U.S. Eighth Air Force for use as heavy bomber bases with the RAF units formerly occupying them being re-allocated places at other RAF bomber airfields, and U.S. Army Engineer Units constructed more airfields to this standard or brought earlier airfields up to this specification by lengthening runways, etc. Many units of the U.S. Ninth Air Force also flew from Class A airfields. The term Class 'A' came about because, quite often, the resultant aerial shot of the crossed runways would look like the letter A.

The specifications set by the British Air Ministry in August 1942 called for three converging strips, each containing a concrete runway optimally placed -- if practicable at the site -- at 60 degree angles to each other in a triangular pattern. The longest strip was designated the main strip and aligned southwest to northeast wherever possible, this being chosen to allow aircraft to take off and land into the prevailing wind. The other two runways were to allow safe takeoff and landing from either end when the wind was blowing from other directions. The primary consideration was for operational safety for any type of aircraft then in operation or under development.

The runways were connected by taxiways called a perimeter track (peri-track), of a standard width of 50 feet (15 m). However, certain stations that were designated to be fighter bases sometimes had a narrower perimeter track, such as RAF Coltishall, whose peri-tracks measured 40 feet (12 m) across. A 30 ft (9.1 m) area was cleared and leveled on either side of the perimeter track. Class A specifications for taxiways set a minimum curve radius of 150 feet (46 m) measured from the centre line for angles greater than 60 degrees and 200 feet (61 m) for angles less than 60 degrees. Perimeter track gradients could not exceed 1 in 40 in any direction, and no building could be placed closer than 150 feet (46 m)from the edge of the track.

...
Wikipedia