Answer based on context:

Increased attention to conventional strength complemented these special forces preparations. In this instance he called up reserves and also proceeded to expand the regular armed forces. Whereas active duty strength had declined from approximately 3,555,000 to 2,483,000 between 1953 (the end of the Korean War) and 1961, it increased to nearly 2,808,000 by June 30, 1962. Then the forces leveled off at around 2,700,000 until the Vietnam military buildup began in 1965, reaching a peak of nearly 3,550,000 by mid-1968, just after McNamara left office.

During which wars was the number of active duty people approximately 3,555,000?
Korean War