From the beginning of "Rolling Thunder", Washington dictated which targets would be struck, the day and hour of the attack, the number, and types of aircraft and the tonnages and types of ordnance utilized, and sometimes even the direction of the attack. Airstrikes were strictly forbidden within of Hanoi and within of the port of Haiphong. A thirty-mile buffer zone also extended along the length of the Chinese frontier. According to U.S. Air Force historian Earl Tilford:  Targeting bore little resemblance to reality in that the sequence of attacks was uncoordinated and the targets were approved randomly – even illogically. The North's airfields, which, according to any rational targeting policy, should have been hit first in the campaign, were also off-limits. Although some of these restrictions were later loosened or rescinded, Johnson (with McNamara's support) kept a tight rein on the campaign, which continuously infuriated the American military commanders, right-wing members of Congress, and even some within the administration itself. One of the primary objectives of the operation, at least to the military, should have been the closure of Haiphong and other ports by aerial mining, thereby slowing or halting the flow of seaborne supplies entering the north. Johnson refused to take such a provocative action, however, and such an operation was not implemented until 1972. There was also little consultation between Johnson and the military chiefs during the target selection process. Even the chairman of the Joint Chiefs, General Earle G. Wheeler, was not present for most of the critical discussions of 1965 and participated only occasionally thereafter. The majority of strikes during "Rolling Thunder" were launched from four air bases, in Thailand: Korat, Takhli, Udorn, and Ubon. The aircraft refueled from aerial tankers over Laos before flying on to their targets in the DRV. After attacking their targets (usually by dive-bombing) the strike forces would either fly directly back to Thailand or exit over the relatively safe waters of the Gulf of Tonkin. It was quickly decided that, in order to limit airspace conflicts between air force and naval strike forces, North Vietnam was divided into six target regions called "route packages", each of which was assigned to either the air force or navy and into which the other was forbidden to intrude. Navy strikes were launched from the aircraft carriers of Task Force 77, cruising off the North Vietnamese coast at Yankee Station. Naval aircraft, which had shorter ranges (and carried lighter bomb loads) than their air force counterparts, approached their targets from seaward with the majority of their strikes flown against coastal targets.