Vraciu was born in East Chicago, Indiana, of Romanian immigrant parents. He graduated from DePauw University in Greencastle, Indiana, and began his military career in 1941, when he enlisted in the U.S. Navy. During his military service in World War II, Vraciu flew Grumman F6F Hellcats in the Pacific, spending five months as a wingman to his mentor, Edward "Butch" O'Hare, the navy's first ace of the war. Vraciu's greatest success took place on June 19, 1944, during what became known as the "Great Marianas Turkey Shoot," when he engaged a Japanese bomber formation in air-to-air combat, downing six Japanese aircraft in eight minutes using only 360 rounds of ammunition. In December 1944 Vraciu was shot down during a mission over the Philippines, he parachuted and spent five weeks with Filipino resistance fighters before rejoining American military forces and returning to . Vraciu spent the last few months of the war serving at the Naval Air Test Center in Patuxent, Maryland.
