William J. Perry, who served as defense secretary from 1994-97, was in the Army's enlisted ranks from 1946-47 and served in Japan as a member of the American occupation force, according to a biography on the website of Stanford University, where he is affiliated with the Freeman Spogli Institute for International Studies.
Perry was given an honorable discharge from the Army, then was commissioned through the Reserve Officer Training Corps at Stanford and served in the Army Reserve from 1950-55 as a second lieutenant.
According to a Pentagon historical office's biographical sketches of all 23 men who have served as defense secretary since the position was created in 1947, three others served in the enlisted ranks and later became commissioned officers -- Melvin Laird in the Navy and Elliot Richardson and Caspar Weinberger in the Army.
So Hagel would be the only defense secretary who ended his military career in the enlisted ranks - he served in Vietnam as a sergeant in 1967-68 and was wounded twice - but one of several who spent time at those ranks.
When Obama announced his selection of Hagel at the White House on Jan. 7, he said Hagel's selection as defense secretary would be "historic."
"He'd be the first person of enlisted rank to serve as secretary of defense, one of the few secretaries who have been wounded in war, and the first Vietnam veteran to lead the department."
Asked about Obama's statement, the White House spokeswoman for Hagel's confirmation process, Marie Harf, said Obama was correct because Perry and the other three who initially served in the enlisted ranks later became officers.
"There's a huge difference between servicemen who start off enlisted and become officers, and those who are always only enlisted," Harf said, noting that Hagel is in the latter category. "You're defined by how you end in the military."
Many other secretaries of defense served previously as military officers without prior service in the enlisted ranks, including Donald H. Rumsfeld (Navy), Robert M. Gates (Air Force), and Leon E. Panetta (Army).