were both out of the country. President Richard M. Nixon's first response was to consider a three-day attack by B-52 Stratofortress bombers on Hanoi and the port city of Haiphong. His National Security Advisor, Dr. Henry Kissinger, convinced Nixon to reconsider, since he did not want to jeopardize the formalization of the Strategic Arms Limitation Treaty (SALT I) with the Soviets, that was due to be signed in May. Another stumbling block to the plan was Abrams' desire to utilize the available bombers (with their all-weather capability) to support the ARVN defense. Nixon and Kissinger considered a plan offered by the Joint Chiefs of Staff to be both unimaginative and lacking in aggression. On 4 April, Nixon authorized the bombing of North Vietnam (which had been limited to reprisal raids just above the DMZ) up to the 18th parallel. To prevent a total ARVN collapse and to protect American prestige during the upcoming summit meeting with Soviet general secretary Leonid Brezhnev, Nixon decided to risk a massive escalation of force. Due to the continuous withdrawal of American forces as part of the policy of Vietnamization, at the time of the invasion fewer than 10,000 U.S. combat troops remained in South Vietnam, and most of them were scheduled to leave within the next six months. The number of combat aircraft stationed in Southeast Asia was less than half that of its peak strength in 1968–1969. At the beginning of 1972, the U.S. Air Force (USAF) had only three squadrons of F-4 Phantoms and one squadron of A-37 Dragonflys, a total of 76 aircraft, stationed in South Vietnam. Another 114 fighter-bombers were located at bases in Thailand. 83 B-52s were stationed at U-Tapao RTAFB, Thailand and at Andersen Air Force Base, Guam. The U.S. Navy (USN)'s Task Force 77 (stationed in the Gulf of Tonkin), had four aircraft carriers assigned to it, but only two were available at any one time to conduct operations. Their air wings had approximately 140 aircraft. Build-up and air attacks American and Republic of Vietnam Air Force (RVNAF) aircraft had been supporting the defense (weather permitting) since the beginning of the offensive. These strikes were conducted in support of ARVN forces, and included those of the air wings of the carriers and . The bad weather limited the ability of the U.S. aircraft to assist in stemming the North Vietnamese onslaught. By 6 April, at naval and