Harry Mattingly was born on August 1, 1942, in Baltimore, Maryland. He enlisted in the U.S. Navy Reserve on August 27, 1959, and went on active duty to begin basic training on January 27, 1960. After completing basic training at NTC Great Lakes, Illinois, in March 1960, Mattingly attended Submarine School at Naval Submarine Base New London, Connecticut, from March to November 1960, and then served aboard the auxiliary research submarine USS Crevalle (AGSS-291) from November 1960 to May 1961. His next assignment was aboard the destroyer USS Harlan R. Dickson (DD-708) from May 1961 to May 1962, followed by Underwater Demolition Team Replacement training with Class 27 (East Coast) at NAB Little Creek, Virginia, from May to November 1962. Petty Officer Mattingly served with UDT-21 at NAB Little Creek until he left active duty and went into the Navy Reserve on August 1, 1963. He returned to active duty in the Navy on September 28, 1965, and served with SEAL Team TWO at NAB Little Creek from October 1965 until he was killed in action in South Vietnam on January 16, 1969. During this time, Petty Officer Mattingly served in combat in South Vietnam from January to June 1967, and again from November 1968 until his death.

His 2nd Bronze Star Medal w/Valor Citation reads:

For meritorious service in connection with operations against the enemy from 1 November 1968 to 16 January 1969 as advisor to a Vietnamese military unit in Chuong Thien Province, Republic of Vietnam. Petty Officer MATTINGLY trained, supervised and directed over one hundred personnel in conducting paramilitary night operations against the Viet Cong infrastructure. Under his leadership, the Chuong Thien force was molded into one of the most effective small military units in the province; one which was highly respected by both military and the civilian community. During this period, Petty Officer MATTINGLY participated in over forty combat operations, and often engaged in fierce battles against the enemy. He was mortally wounded on 16 January 1969 while leading his unit in an attack against a heavily armed Viet Cong force. His outstanding performance of duty significantly contributed to a highly efficient and combat ready Vietnamese military unit. Petty Officer MATTINGLY's exceptional leadership, devotion to duty and courage under fire were in keeping with the highest traditions of the United States Naval Service.

The Combat "V" is authorized.