SPARS was the official nickname for the United States Coast Guard (USCG) Women's Reserve. The nautical acronym was derived from the USCG's motto, Latin: "Semper Paratus"—"Always Ready" (SPAR). The Women's Reserve was established by law in November 1942 during World War II. 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.

Officer candidates for the Women's Reserve needed to be age 20–50, and they were required to have a college degree or two years of college and two years of professional or business experience. For enlisted personnel, the qualifying age was 20–36, and they were required to have completed at least two years of high school. At first the USCG would not accept African American women, but in February 1945 five African American women were accepted and served in the SPARs. Officer candidates received their indoctrination at Smith College in Northampton, Massachusetts, and later at the USCG Academy in New London, Connecticut. Enlisted personnel first received training on several college campuses. Later, their training took place at Palm Beach, Florida, in the Biltmore Hotel that was remodeled for use as a training center. Toward the end of the war, training of enlisted personnel was transferred from Palm Beach to Manhattan Beach, Brooklyn, New York.

At peak strength, the Women's Reserve had approximately 11,000 officers and enlisted personnel in its ranks. Except for the territory of Puerto Rico, the SPARs served in every USCG district, including the then territories of Hawaii and Alaska. Most officers were general duty officers, and most enlisted women performed clerical duties. Nonetheless, a select group of officers and enlisted SPARs were chosen to work with LORAN (Long Range Aid to Navigation); it was a secret land-based navigation system developed during World War II at the Massachusetts Institute of Technology (MIT) to monitor the location of ships at sea or aircraft in flight.

Following the Victory over Japan (V-J Day) in August 1945, the demobilization of SPAR personnel began. By 1946, nearly all reservists had been discharged, and in 1947 the Women's Reserve was officially inactivated. But on the eve of the Korean War in November 1949, the Women's Reserve was reactivated—this time as the USCG Women's Volunteer Reserve. Throughout the conflict in Korea (1950–1953), the USCG actively recruited former SPARs for the volunteer reserve with approximately 200 of them reenlisting. In 1973, Congress enacted legislation ending the Women's Volunteer Reserve, and allowing women to be officially integrated into either active-duty or reserve service.

Prior to World War II, the United States Coast Guard was the smallest of the U.S. military branches and had operated under the auspices of the U.S. Department of the Treasury. This changed on November 1, 1941, when Executive Order 8929 issued by President Franklin D. Roosevelt directed the Coast Guard to operate as part of the Navy; placing it under the supervision of the U.S. Secretary of the Navy. Following its transfer, the Coast Guard began expanding with personnel needs increasing exponentially, and it sought to allow women to serve in the USCG Reserve. In November 1942, the USCG Women's Reserve Act was passed by the U.S. Congress and signed into law by President Roosevelt on November 23. The law amended the USCG Auxiliary and Reserve Act of 1941 in order to "expedite the war effort by providing for releasing officers and men for sea duty and replacing them with women in the shore establishment of the Coast Guard and for other purposes." The new law established the Women's Reserve as a branch of the U.S. Coast Guard Reserve. It gave the Women's Reserve the authority to enlist and appoint women to serve during World War II and for six months thereafter (or until such earlier time when Congress, or the president, might choose to end this authority). All women reservists would be trained and qualified for duty at USCG continental shore stations, and the Coast Guard was forbidden from using women reservists to replace civil service personnel. The USCG legislation was similar to an earlier law that created the Women Accepted for Volunteer Emergency Service, better known as the WAVES.

Initially, women serving in the USCG Reserve were only to be stationed in the continental United States, but in 1944 they were allowed to deploy to Hawaii and Alaska (then U.S. territories).

Dorothy C. Stratton had been the dean of women at Purdue University when World War II began. She earned her MA degree from the University of Chicago and her PhD from Columbia University. In her capacity at Purdue, Stratton was asked by the U.S. Army to recommend candidates to become the first female officers commissioned by the Women's Army Corps (WACS). At the same time, a Purdue colleague—who was working with the U.S. Navy in a similar recruitment program—encouraged Stratton to apply for a commission in the newly formed WAVES. Stratton thought this might be a good way to serve her country, so she applied and was accepted, and Purdue granted her an extended leave of absence. On August 26, 1942, Stratton reported to Northampton, Massachusetts, joining the first class of female officer candidates for the WAVES. Upon graduation, she was commissioned a senior-grade lieutenant.

Stratton's first duty assignment with the WAVES was at the University of Wisconsin. With barely enough time to settle into her new duties, she was contacted by the Bureau of Naval Personnel to report to Washington D.C. without delay. In the Nations' Capitol, Stratton met with several high-ranking USCG officers who informed her of pending legislation to establish a women's reserve branch within the Coast Guard and that she had been recommend for its directorship. The legislation passed and it was signed into law on November 23. The following day, Stratton was sworn into the USCG as lieutenant commander and as the director of the SPARs. She would later be promoted to commander and to captain.