 Although the initial American commitment to the war in Vietnam had been limited to advice and materiel support, by 1964 there were 21,000 US advisors in South Vietnam. However, with the Army of the Republic of Vietnam (ARVN) weakened by successive defeats at the hands of the communists, the South Vietnamese government faltering, and Saigon threatened with a major offensive, the worsening situation led to a significant escalation of the war in 1965, with a large-scale commitment of US ground troops under the command of General William Westmoreland. At first the Americans had adopted a cautious strategy, applied to the strictly limited role of base defence by US Marine units. This was abandoned in April 1965, and replaced by a new "enclave strategy" of defending key coastal population centres and installations. This strategy required the introduction of nine additional US battalions, or 14,000 troops, to bring the total in Vietnam to 13. Allied nations of the Free World Military Forces were expected to contribute another four battalions.
