When WWII war movies were made in the immediate decades afterwards there was enough existing materiel to provide for many movies. Catch-22, filmed in the late '60s, found enough working, flyable B-25, to fill a squadron. This was beyond military surplus that dressed their set. Other movies were made with authentic equipment to save money not stress realism. Now such film must be shot as period pieces with nearly everything reproduced at enormous cost and bother.