the intensity of the bombing campaign was reflected by the sharp increase in the number of strike and support sorties flown in southeast asia as a whole: from 4,237 for all services, including the vnaf, during the month preceding the invasion, to 27,745 flown in support of arvn forces from the beginning of april to the end of june (20,506 of them flown by the air force). b-52s provided an additional 1,000 sorties during the same period. the north was feeling the pressure, admitting in the official pavn history that "between may and june only 30 percent of supplies called for in our plan actually reached the front-line units." in total, 41,653 "linebacker" missions dropped 155,548 tons of bombs.