Thrash was awarded his first Legion of Merit with Combat "V" and his sixth and seventh Air Medals prior to being captured and imprisoned by the Chinese Communists in December 1951. Following his repatriation in September 1953, he returned to the United States and was subsequently assigned as executive officer, and later, commander of Marine Wing Service Group 37. From May 1955 to July 1958, he was attached to the Division of Aviation, Headquarters Marine Corps, serving consecutively as assistant head, and head, Plans and Readiness Branch, and deputy assistant director of aviation. While there, he was promoted to colonel in November 1955. In June 1959, he completed the National War College in Washington, D.C.