Calvin Graham
Calvin Leon Graham was the youngest U.S. serviceman to serve and fight during World War II. Following the attack on Pearl Harbor, he enlisted in the United States Navy from Houston, Texas on August 15, 1942, at the age of 12. His case was similar to that of Jack W. Hill, who was granted significant media attention due to holding service number one million during World War II, but later was discovered to have lied about his age and subsequently discharged.
Graham was born in Canton, Texas and was attending elementary school in Houston before he decided to join the Navy, after his father had died and his mother had remarried.
Source: Wikipedia