ordnance. From the beginning of Freedom Train in April to the end of June 1972 the United States lost 52 aircraft over North Vietnam: 17 to missiles; 11 to anti-aircraft weapons; three to small arms fire; 14 to MiGs; and seven to unknown causes. During the same time period, the RVNAF lost ten aircraft. 63 VPAF aircraft were destroyed during the same time period. North Vietnam claimed that it had shot down 651 aircraft and sunk or set on fire 80 U.S. warships during the operation. 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. USAF 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 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. North Vietnamese aircraft losses (Air-to-air losses only) U.S. aircraft losses during Linebacker Between 10 May and 23 October 1972, the United States lost a total of 134 aircraft either over the north or as a direct result of Linebacker missions. 104 were lost in combat and 30 were destroyed in operational accidents. Losses by service were: USAF: – 70 total 51 combat losses (22 to MiGs, 5 induced losses, 20 to AAA, 4 to SAMs) 43 F-4D/E Phantom II (+17 non-combat losses) 2 RF-4C Photo Recon (+1 non-combat loss) 4 F-105G Wild Weasel (+1 non-combat loss) 2 F-111A "Aardvark" USN: – 54 total 43 combat losses (4 to MiGs, 2 induced, 13 SAM, 27 AAA) 8 F-4B/J Phantom II (+3 non-combat losses) 22 A-7A/C/E Corsair II (+3 non-combat losses) 3 A-6A Intruder 2 F-8J Crusader (+3 non-combat losses) 5 A-4F Skyhawk (+1 non-combat loss) 1