Description President Nixon responded to this invasion with "Operation Freedom Train", which called for the renewal of general air strikes throughout North Vietnam above the 20th parallel for the first time since 1968. The North Vietnamese invasion prompted increased air operations by the carriers in support of South Vietnamese and US forces. The carriers on Yankee Station when North Vietnam invaded on 30 March were Hancock and Coral Sea. During the March four carriers had rotated on Yankee Station; they were Constellation, Kitty Hawk, Coral Sea and Hancock.
Operation Freedom Train involved Navy tactical air sorties against military and logistic targets in the southern part of North Vietnam which were involved in the invasion of SVN. The operating area in North Vietnam was initially limited to between 17th and 19th parallel. However, special strikes were authorized against targets above the l9th parallel on various occasions. The magnitude of the North Vietnam offensive indicated that an extended logistics network and increased resupply routes would be required to sustain ground operations by North Vietnam in their invasion of South Vietnam. Most target and geographical restrictions that were placed in effect since October 1968 concerning the bombing in North Vietnam were gradually lifted and the list of authorized targets expanded. Strikes in North Vietnam were against vehicle targets, lines of communication targets (roads, waterways, bridges, railroad bridges and railroad tracks), supply targets, air defense targets and industrial/power targets. Aircraft involved in Freedom Train operations were from Hancock, Coral Sea, Kitty Hawk and Constellation. By the end of April operations were permitted in North Vietnam throughout the region below the 20th parallel and many special strikes above the 20th parallel had also been authorized.
The aerial interdiction campaign against North Vietnam which began on 6 April 1972 with attacks in the southern part of the country expanded rapidly. Inclement weather along most bombing runs caused pilots to use precision instruments to destroy the targets during early April. However, once the weather cleared, visual strikes resumed, and the wing sent more and more aircraft into North Vietnam. The pilots on bombing runs were tasked to cut lines of communication and destroy transportation resources and surface-to-air missile sites.
On 16 April, B-52s, escorted by fighter and aircraft specializing in electronic countermeasures and suppression of surface-to-air missiles, bombed the fuel storage tanks at Haiphong, setting fires that, reflected from cloud and smoke, were visible from 110 miles away. Shortly afterward, carrier aircraft joined Air Force fighter-bombers in battering a tank farm and a warehouse complex on the outskirts of Hanoi. When these attacks failed to slow the offensive, naval aircraft began mining the harbors on 8 May, and two days later the administration extended the aerial interdiction campaign, formerly known as Freedom Train but now designated Linebacker, throughout all of North Vietnam.
