Complex sentence: The total of 31 Inland Aircraft Fuel Depots were in operation by May 1944 and all IAFD sites were located on railway lines for access by rail tankers, but were situated well away from the airfields they serviced as these were bulk storage facilities.
Split into simpler sentences: The total of 31 Inland Aircraft Fuel Depots were in operation by May 1944. All IAFD sites were located on railway lines for access by rail tankers, but were situated well away from the airfields they serviced as these were bulk storage facilities.