United States Marine Corps Women's Reserve (Reserve) was the World War II women's branch of the United States Marine Corps Reserve. It was authorized by the U.S. Congress and signed into law by President Franklin D. Roosevelt on 30 July 1942. Its purpose was to release officers and men for combat, and to replace them with women in U.S. shore stations for the duration of the war plus six months. Ruth Cheney Streeter was appointed the first director. The Reserve did not have an official nickname as did the other World War II women's military services.

SPARS was the authorized nickname for the United States Coast Guard (USCG) Women's Reserve. The nickname is an acronym fashioned from the USCG's motto, "Semper Paratus"—"Always Ready" (SPAR). The Women's Reserve was established by the U.S. Congress and signed into law by President Franklin D. Roosevelt on November 23, 1942. The law authorized the USCG to accept women into its Women's Reserve as commissioned officers and at the enlisted level for the duration of World War II plus six months. Its purpose was to release male officers and enlisted men for sea duty by replacing them with women at shore stations. This same month, Dorothy C. Stratton was appointed director of the Women's Reserve and given the rank of lieutenant commander. She was later promoted to captain.