during and immediately following the pavn offensive, u.s. air force, navy, and marine corps aviators had flown 18,000 sorties in the four northern provinces of south vietnam and dropped 40,000 tons of ordnance in the battle of an lộc. between march and may, b-52 sortie rates had climbed from 700 to 2,200 per month and they had dropped 57,000 tons of bombs in quảng trị province alone. during "freedom train" and "linebacker" proper, b-52s had dropped 150,237 tons of bombs on the north while air force and navy tactical aircraft had flown 1,216 sorties and dropped another 5,000 tons of ordnance.