"linebacker" had played a crucial role in blunting the northern offensive by drying up its vital sources of supply. pavn had evolved into a conventional military force, and such a force depended upon a complex logistical system, which made it vulnerable to aerial attack. by september, imports into north vietnam were estimated at 35 to 50 percent below what they had been in may, bolstering claims that the campaign had been successful in its interdiction effort. air force general robert n. ginsburgh, of the office of the secretary of the air force, summed up the attitudes of u.s. commanders by remarking that "linebacker" had "a greater impact in its first four months of operation than "rolling thunder" had in three and one-half years." although henry kissinger may have announced that peace was at hand, it was not going to come easily. american bombers would once again return to the skies of north vietnam in 1972 during operation linebacker ii before the american commitment to the vietnam war came to an end.