Boomer saw combat action from 1966 to 1967 in the Republic of Vietnam as the Commanding Officer, Company H, 2nd Battalion, 4th Marines. During this combat tour, he was awarded the Silver Star Medal for valor. Returning to the States, he attended the Amphibious Warfare School at Quantico. Upon completion of school, he was promoted to major in May 1968, and was transferred to Headquarters Marine Corps, Washington, D.C., for duty as the Administrative Assistant and Aide-de-Camp to the Deputy Chief of Staff for Plans and Programs. Following this assignment, he attended the Armed Forces Staff College in Norfolk, Virginia.