 The shocks that reverberated from the battlefield continued to widen : On 18 February 1968 MACV posted the highest U.S. casualty figures for a single week during the entire war : 543 killed and 2 @,@ 547 wounded . As a result of the heavy fighting , 1968 went on to become the deadliest year of the war for the US forces with 16 @,@ 592 soldiers killed . On 23 February the U.S. Selective Service System announced a new draft call for 48 @,@ 000 men , the second highest of the war . On 28 February Robert S. McNamara , the Secretary of Defense who had overseen the escalation of the war in 1964 – 1965 , but who had eventually turned against it , stepped down from office . 
