Mary Helen O’Brien was born on May 12th, 1924, in Chicago, IL, to Edward and Anna O’Brien. O’Brien was a second-generation immigrant, with both of her parents having immigrated to the United States from Ireland. O’Brien was seventeen years old when the Empire of Japan attacked the United States Naval Base at Pearl Harbor, triggering US entry into the Second World War. Two years later, O’Brien would join the first generation of female Marines.
The war in the Pacific was beginning to take a heavy toll on the Marine Corps. The result of the Battle of Guadalcanal was a victory for the Marines sent to capture the island from the Japanese, but the casualties were staggering. The top brass of the USMC saw the need to ship as many Marines to combat duty as possible, an effort that would have the unsavory side-effect of leaving these Marines’ current non-combat jobs empty. Their solution was to create the Marine Corps Women’s Reserve (WR), which would see approximately 20,000 women enlist to perform a variety of non-combat tasks:
Women Marines were assigned to over 200 different jobs, including radio operator, photographer, parachute rigger, driver, aerial gunnery instructor, cook, baker, quartermaster, control tower operator, motion picture operator, auto mechanic, telegraph operator, cryptographer, laundry operator, post exchange (store) manager, stenographer, and agriculturist.
According to O’Brien’s future husband James Erwin, she was given the job of mail clerk at the Parris Island Recruit Depot. This position ensured that lines of communication were maintained so that orders could be received and executed throughout the USMC.
After the war, the Women’s Reserve was mostly demobilized and sent home. However, O’Brien was among approximately 1,000 women who were retained in case of an emergency: “On 7 June 1946, Commandant of the Marine Corps Gen Alexander A. Vandegrift approved the retention of a small number of women on active duty. They would serve as a trained nucleus for possible mobilization emergencies.” General Vandegrift’s decision would prove to be prophetic, for on June 25th, 1950, the North Korean Army invaded US ally South Korea. O’Brien was working as a telephone operator at the 9th Marine Corps Reserve District Headquarters, where she worked in the effort to mobilize Marines from the Great Lakes area to Korea. Also working at the Headquarters was James Erwin, who O’Brien began dating. The two eventually married privately, because they thought that they would be unable to get furlough time due to the emergency. However, their first sergeant managed to get them a 72-hour honeymoon when he received news of their marriage, according to Erwin: “So my wife and I are in the hotel there, and the phone rang. And it was the first sergeant. ‘Why in the hell didn’t [you] tell me you were getting married?’ I said, ‘Well, you know, there is no leave or anything like that.’ And he said, ‘Well, you got a 72-hours. That is what I can do for you.’”
In 1951 the Korean War began to wind down, and thus the Marine Corps began to reduce its reserve forces. According to James Erwin, this was when the couple decided to retire from the Corps: “My wife had had enough military life… It was time to go out and think about getting a job and raising a family and so forth. And when they said we could get out, why, we both applied for inactive duty. We weren’t discharged, we were just released from active duty.” The couple raised five children in Madison, Wisconsin, where Mary Erwin spent much of her free time volunteering at the Women’s Marine Association and American Legion Post #501. She passed away unexpectedly on November 23rd, 1997, and was survived by her husband, children, and grandchildren. Mary Helen Erwin leaves behind a legacy of service to her country when women were needed to fill the roles of men in combat, as well as of finesse in her role that helped the United States Marine Corps in its mobilization efforts in the Korean War.