Howard Gilmore was born on September 29, 1902, in Selma, Alabama. He enlisted in the U.S. Navy on November 15, 1920, and received an appointment to the U.S. Naval Academy in June 1922. Gilmore graduated with a commission as an Ensign in June 1926, and his first assignment was aboard the battleship USS Mississippi (BB-41) before going through submarine training in 1930. CDR Gilmore was executive officer and then commanding officer of the submarine USS Shark (SS-174) shortly before the beginning of World War II, and then took command of the submarine USS Growler (SS-215) on December 8, 1941. He commanded USS Shark through four war patrols in the Pacific Ocean, and was killed in action on February 7, 1943.

His Medal of Honor Citation reads:

For distinguished gallantry and valor above and beyond the call of duty as Commanding Officer of the U.S.S. Growler during her Fourth War Patrol in the Southwest Pacific from 10 January to 7 February 1943. Boldly striking at the enemy in spite of continuous hostile air and antisubmarine patrols, Commander Gilmore sank one Japanese freighter and damaged another by torpedo fire, successfully evading severe depth charges following each attack. In the darkness of night on 7 February, an enemy gunboat closed range and prepared to ram the Growler. Commander Gilmore daringly maneuvered to avoid the crash and rammed the attacker instead, ripping into her port side at 11 knots and bursting wide her plates. In the terrific fire of the sinking gunboat's heavy machineguns, Commander Gilmore calmly gave the order to clear the bridge, and refusing safety for himself, remained on deck while his men preceded him below. Struck down by the fusillade of bullets and having done his utmost against the enemy, in his final living moments, Commander Gilmore gave his last order to the officer of the deck, "Take her down." The Growler dived; seriously damaged but under control, she was brought safely to port by her well-trained crew inspired by the courageous fighting spirit of their dead captain.