Julia Hamblet, a retired colonel who was instrumental in integrating women into the regular Marine Corps in the late 1940s and became the longest-serving director of the women’s branch of the Marines, died April 17 at a retirement community in Williamsburg, Virginia. She was 100.

The specific cause of death could not be immediately determined, said a niece, Doreen Hamblet.

After working in Washington, D.C., for several years with the old U.S. Information Service, Col. Hamblet joined what was then called the Marine Corps Women’s Reserve in 1943.

She was among the first women sworn in as commissioned officers during World War II. She said she joined the Marine Corps because she had one brother in the Army and another in the Navy and wanted to be impartial.

More than 20,000 women served as Marines during World War II, but the women’s branch was officially part of the reserves and was separate from the regular Marine Corps. Other women’s military branches had acronyms, such as the Navy’s WAVES (for Women Accepted for Volunteer Emergency Service) or the WACs (Women’s Army Corps), but there was no shorthand for female Marines.

“They don’t have a nickname and they don’t need one,” Marine Corps Commandant Thomas Holcomb told Life magazine in 1944. “They get their basic training in a Marine atmosphere at a Marine post. They inherit the traditions of Marines. They are Marines.”

Soon after she was commissioned, Col. Hamblet was named adjutant to Col. Katherine Towle, the director of Women Marines, and served at bases in California, North Carolina and Virginia.

Most female Marines held clerical and administrative jobs, but others worked as radio operators, photographers, control tower operators, weather observers, musicians, statisticians, journalists and cryptographers. At the end of the war in 1945, Col. Hamblet — then holding the rank of major — commanded 2,600 women in an aviation group at Cherry Point, North Carolina.

“For some time, I had mixed feelings about the appropriateness of women serving in the regular Marine Corps,” Col. Hamblet said in a 2004 interview for the Women In Military Service For America Memorial Foundation. “All Marines, officers and enlisted, were trained to fight … an assignment legally prohibited to servicewomen.”

In 1946, Col. Hamblet was named director of the Women’s Reserve, but postwar demobilization saw the ranks of female Marines dwindle to fewer than 200.

“I discovered that we could not get the active duty leaders we wanted for our reserve units,” she said, “without providing them the security of the regular service.”

The Women’s Armed Services Integration Act was passed in 1948, which made women full-fledged Marines, although they remained in separate units from the men for decades. Female officers could not hold a rank higher than colonel.

By 1953, when Col. Hamblet succeeded Towle as director of Women Marines, she commanded a corps of more than 2,700 female troops. Typical of the news coverage of the time, reporters commented on Col. Hamblet’s age (36) and appearance. Time magazine described her as a “girl who was born to pose for a recruiting poster.”

During the six years she led Women Marines, Col. Hamblet appeared on the nationally televised game shows “What’s My Line?” and “To Tell the Truth.” She voluntarily stepped down in 1959 because “I was blocking other women officers for promotion.”

She later became a military adviser to the commander in chief of allied forces in southern Europe and led a training unit at Parris Island, South Carolina, before retiring from the Marine Corps in 1965. Her decorations included the Legion of Merit.

Julia Estelle Hamblet was born Mary 12, 1916, in Winchester, Massachusetts. Her father was a chemical engineer.

Known to her family as Judy, she graduated in 1937 from Vassar College in Poughkeepsie, New York, then worked for six years with the U.S. Information Service. She received a master’s degree in public administration from Ohio State University in 1951.

After her military career, Col. Hamblet spent 13 years as an official with the U.S. Office of Education (later the Education Department). She was based for several years in Seattle, where she supervised a federal student loan program in the Northwest.

She retired to Alexandria, Virginia, where she volunteered with the American Red Cross and YWCA and was an elder at Alexandria’s Old Presbyterian Meeting House. She moved to Williamsburg in 1986.

She had no immediate survivors.

Col. Hamblet often reminisced with her nieces and nephews about her career in the Marine Corps, calling it “a decision I never regretted in 22 years of active duty.”