Leonard E. Rea was born on March 14, 1897, in Auburn in New York, and, after graduation from high school, decided to enlist in the United States Marine Corps on April 19, 1917.

He participated in the Battle of Saint-Mihiel in September 1918 and was appointed commander of a combat liaison group between the 5th Marine Regiment and the 5th Infantry Division on the right flank of the defensive line.

[1][2] Rea led his platoon in the Battle of Blanc Mont Ridge at the end of October 1918 and was wounded by enemy machine gun fire.

Rea was ordered to Washington, D.C., where he was appointed assistant to the officer in charge of the supply division of the Quartermaster Department under General Seth Williams at Headquarters Marine Corps.

[3] On his return to the United States, Rea was assigned back to the Headquarters Marine Corps in Washington, D.C. and appointed executive officer at the Quartermaster Department.