Ensign Coulter's first assignment was on the battleship USS Pennsylvania and he later served as an Engineer aboard the destroyer-minesweeper USS Perry. When the Japanese attacked Pearl Harbor on 7 December 1941, he was serving aboard the destroyer USS Alden in waters off the Philippines and Indonesia. While on the Alden, Coulter was promoted to Lieutenant and served as Engineering Officer. In February 1942, the Alden participated in the seven-hour Battle of the Java Sea, where the Japanese Imperial Navy sank five Allied ships and defeated the Allied fleet. Luckily for Coulter, the Aiden was one of the few ships that survived the Battle.
In late 1942, Coulter's request to join the submarine service was granted and he was assigned to the Navy Submarine School in New London, CT. Upon graduation, he joined the crew of the submarine USS Skipjack in the Pacific Theatre during five War Patrols. During his 42 months aboard the Skipjack, he served as Torpedo and Gunnery Officer and later, as Executive Officer. In March 1944, he was promoted to Lieutenant Commander and assumed command of the Skipjack, a position he held for 20 months.
The Skipjack was decommissioned and became a target ship as part of the Operation Crossroads atom bomb tests at Bikini Atoll in 1946. Skipjack survived the first atomic explosion, which was 500 feet above the boat. The second blast was detonated underwater and sunk the Skipjack and seven other vessels. Coulter and others in his crew were allowed to observe the sinking.
Coulter later commanded the submarine USS Bugara before he was assigned to the U.S. Naval Academy, where he was a Battalion Officer and Leadership Instructor.
During his naval career, he served as commanding officer of two submarines and four surface ships. He was also Commanding Officer of the U.S. Naval Advisory Group in Korea, where he served from 1963-65. Captain Coulter retired from active duty in 1969, following a tour as Director of Navy Recruiting in New York and New England. Over his 30-year career, he served either abroad, or aboard ship, for nearly 15 years.