The 91st Engineer Battalion was a military engineer unit in the United States Army. The battalion, which was composed mainly of African-American troops, served during in the Pacific Theater of Operations during World War II, when it was known as the 91st Engineer General Service Regiment. After the war, the unit was deactivated as part of the demobilization process. It was reactivated in 1952 and remained in existence until the early 1970s. In 1991 it was reactivated, after which it was employed on operations in Yugoslavia, Kuwait, Chad and Iraq before being deactivated again in 2005.