From 1940 to 1942, Weyand was assigned to active duty and served with the 6th Field Artillery. He graduated from the Command and General Staff College at Fort Leavenworth in 1942 and served as adjutant of the Harbor Defense Command in San Francisco from 1942 to 1943. He moved on to the Office of the Chief of Intelligence for the US War Department General Staff in 1944. He became assistant chief of staff for intelligence in the China-Burma-India Theater from 1944 to 1945. In the immediate aftermath of the war he was in the Military Intelligence Service in Washington, D.C. from 1945 to 1946.