Despite their size , however , RVNAF operations were severely curtailed Cause_change_of_position_on_a_scale due Causation to cutbacks in U.S. military aid .

Furthermore , the RVNAF were prevented Preventing_or_letting from undertaking reconnaissance Scrutiny and ground support Supporting missions due to the threat posed Causation by formidable anti-aircraft weapons deployed Arranging by North Vietnam .

When the North Vietnamese military renewed Recovering their offensive early in 1975 , the RVNAF was handicapped Hindering and many of their aircraft were either lost Earnings_and_losses or captured Conquering as formations of the People 's Army of Vietnam ( PAVN ) swept Scrutiny through the Central Highlands of South Vietnam .