The shock of the Spring Invasion and the failure of South Vietnamese forces to hold back the invaders without American assistance resulted in the resumption of US bombing raids on North Vietnam.  The limited Freedom Train operation that commenced on 5 April 1972 had little obvious effect so President Nixon decided on a large-scale campaign against the North, code named Linebacker, which started on 10 May.  The campaign was later known as Linebacker I and ended on 23 October.

The aims of the campaign were to restrict supplies entering North Vietnam from abroad; to destroy military targets and stockpiles of supplies within North Vietnam; and to restrict the flow of supplies throughout North Vietnam and along the the Ho Chi Minh Trail into South Vietnam.  The major difference between Linebacker I and Rolling Thunder was the decision to mine North Vietnam’s major ports.  Operation Pocket Money was initiated on 9 May when A-6s and A-7s from the USS Coral Sea dropped mines in the waterways leading to Haiphong Harbour.  In addition, the harbours at Cam Pha, Hon Gay, Vinh and Thanh Hoa were also mined.  All the mines were set to become live at 6.00pm Hanoi time on the 11th thereby giving foreign ships the opportunity to leave the mined harbours safely until that time.

The day after the mining operation commenced the bombing of North Vietnam resumed with a vengeance.  The Navy made the first strikes when about 90 aircraft from the Coral Sea, Constellation and Kitty Hawk attacked POL, railway and bridge targets in and around Haiphong.  Between 6 April and the end of June the USAF’s 8th TFW had destroyed 106 bridges in North Vietnam, including the Paul Doumer and Thanh Hoa bridges, using the new laser-guided bombs for the first time in the North.  North Vietnamese opposition to the new campaign was vigorous.  In addition to a huge increase in the number of anti-aircraft guns that now faced the US aircrew, the VPAF’s MiGs also put up strong resistance.  However, the US fighter crews now had the upper hand.  The new air combat training programme that had been instituted by the US Navy resulted in improved tactics and a greater level of exposure to realistic air combat training for the fighter crews.  The introduction of the APX-80 Combat Tree equipment allowed USAF F-4’s to interrogate the MiG’s IFF and verify that a distant radar target was an enemy aircraft which resulted in a major advantage for US pilots.  On 10 May USAF and Navy Phantoms shot down a total of 11 MiGs for the loss of just two USAF F-4s to the enemy aircraft.