He was promoted to major in March 1940 and to lieutenant colonel in December 1941, the latter coming while he was in Panama as commanding officer of the 16th Pursuit Group and chief of staff of the 6th Air Force. Weyland was promoted to colonel in March 1942 and returned to Washington in June as deputy director of air support at Headquarters Army Air Force. He was advanced to brigadier general in September 1943 and in November went to Europe as command general of the 84th Fighter Wing. Four months later he became command general of the XIX Tactical Air Command. Under him this combat unit gained fame for its close air support of General George Patton's U.S. Third Army in the successful movement across France in August 1944 and Germany in the spring of 1945. By January 1945 Weyland had become a major general and finished the air war against Germany, participating in six major campaigns and called by Patton "the best damn general in the Air Corps."
Returning to the United States in September 1945, Weyland served for nine months as Assistant Commandant of the school at Fort Leavenworth, Kansas, and in June 1946 went to Washington as Assistant Chief of Plans at Headquarters Army Air Force. He moved to Plans and Operations when the Air Force became a separate service. From February 1948 to July 1950, he served as Deputy Commandant of the National War College in Washington.
Korean War
In July 1950 he was briefly commanding general of Tactical Air Command until going to Headquarters Far Eastern Air Force in Tokyo as vice commander for operations in the first full month of the Korean War. In April 1951, he returned to Tactical Air Command and was promoted to lieutenant general. In June 1951, he went back to Tokyo as commanding general of Far Eastern Air Forces and the United Nations Air Forces when Lieutenant General George Stratemeyer had a heart attack. Weyland's widely recognized ability and experience in tactical warfare was demonstrated in 10 major campaigns in Korea. He was promoted to four-star general on July 5, 1952. He stayed in Japan to help that nation reorganize its air defense forces and aircraft industry, and became known as the "father of the new Japanese air force."
Post-Korean war service and retirement
Weyland returned to the United States in May 1954 to serve as Commanding General of Tactical Air Command. He retired from the Air Force on July 31, 1959. He died on September 2, 1979.
Awards and decorations
During his career, he earned many decorations, including two Distinguished Service Medals, the Silver Star, the Distinguished Flying Cross, the Legion of Merit, Bronze Star, and Air Medal, as well as awards from Great Britain, France, Luxembourg, Belgium, Korea, Thailand, the Philippines, Japan and Brazil.