Diem's hold had slackened so much by the end of the year that alarms sounded in Washington. In early 1962, the US began sending advisors and helicopters to Vietnam in fairly large numbers. These and Diem's strategic hamlet program held the Viet Cong for a time in check. But not for long, because the Communists re¬gained their momentum in early 1963, and South Vietnam resumed its downhill slide. The decline quickened with Diem's assassination on 1 November