Pressures other than those produced by military events in the South were also working to move the United States toward direct military intervention against the Communists in Indochina. Although sustained open warfare had not occurred as a result of the Tonkin Gulf crisis of early August, tensions continued to mount between North Vietnam and the United States throughout the autumn. On 1 November, just after the cessation of the U.S. air strikes which followed the Tonkin Gulf incidents, Viet Cong mortar squads attacked American facilities at the Bien Hoa airbase near Saigon. Four American servicemen were killed, five B-57 medium bombers destroyed, and eight others heavily damaged in the raid. President Johnson’s reaction to the Bien Hoa attack was to initiate a month-long review of U.S. policy regarding North Vietnam. In early December that review culminated in the adoption of a two-phased plan to discourage further North Vietnamese support of the Viet Cong by expanding the air war. Phase I, approved for implementation in December, called for stepped-up air operations against the vital Communist infiltration routes in Laos, and for the intensification of covert operations against North Vietnam. Approved “in principle,” Phase II involved “a continuous program of progressively more serious air strikes” against North Vietnam. The implementation of Phase II, it was agreed, would depend on future enemy actions.[13-3] As if to indicate that Communist policy makers had settled on a parallel course of escalation, Viet Cong terrorists bombed a U.S. officers’ quarters in Saigon on Christmas Eve, killing two Americans and wounding over 50 others.[13-A] [13-A] Among the wounded was Major Damm, the Assistant Senior Marine Advisor. The new year, 1965, would open against this portentous combination of intensified U.S. air activities over Laos, a worsening military situation on South Vietnam’s battlefields, and the existence of the Phase II contingency plans. It was this situation which would spawn a new series of events as the first months of 1965 unfolded--events which would determine the direction of American and North Vietnamese military involvement in the war for South Vietnam. In January, MACV intelligence would learn that two new North Vietnamese Army regiments, the _32d_ and the _101st_, had infiltrated the South and had initiated combat operations. Intelligence sources would also report the existence of another NVA regiment in the first stages of formation in Quang Tri Province. When added to a unit of similar size which had appeared in Kontum Province (II Corps Tactical Zone) in the final weeks of 1964, the new arrivals would raise to four the number of North Vietnamese regiments known to be operating on South Vietnamese soil.[13-4]