John was born on the 11th of September 1901, in Henry, Illinois, and after high school he was appointed to, and attended, the US Naval Academy. He graduated the Academy in June of 1924 and first served on the battleship USS Maryland before then being assigned to the USS S-24 in 1927. John became an instructor of diesel engineering and by 1936, he was a Lieutenant in command of the USS S-20. He was assigned to the Bureau of Engineering and Bureau of Ships in Washington DC as a Lieutenant Commander until 1941, when John became the engineer officer for the Pacific Fleet submarine force.

During John’s first war patrol in 1942, he was a Captain on board the USS Sculpin and was part of the decision-making process of whether, or not, to form a wolfpack for the mid-Pacific. A wolfpack was a tactic used by submarines to attack convoys and were very successful against the Japan’s merchant marines. It was during an attack on a Japanese convoy that would cost John his life and earn him the Medal of Honor. The citation reads:

For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty as commander of a submarine coordinated attack group with flag in the U.S.S. Sculpin, during the 9th war patrol of that vessel in enemy-controlled waters off Truk Island, 19 November 1943. Undertaking this patrol prior to the launching of our first large-scale offensive in the Pacific, Capt. Cromwell, alone of the entire Task Group, possessed secret intelligence information of our submarine strategy and tactics, scheduled Fleet movements, and specific attack plans. Constantly vigilant and precise in carrying out his secret orders, he moved his undersea flotilla inexorably forward despite savage opposition and established a line of submarines to southeastward of the main Japanese stronghold at Truk. Cool and undaunted as the submarine, rocked and battered by Japanese depth charges, sustained terrific battle damage and sank to an excessive depth, he authorized the Sculpin to surface and engage the enemy in a gunfight, thereby providing an opportunity for the crew to abandon ship. Determined to sacrifice himself rather than risk capture and subsequent danger of revealing plans under Japanese torture or use of drugs, he stoically remained aboard the mortally wounded vessel as she plunged to her death. Preserving the security of his mission, at the cost of his own life, he had served his country as he had served the Navy, with deep integrity and an uncompromising devotion to duty. His great moral courage in the face of certain death adds new luster to the traditions of the U.S. Naval Service. He gallantly gave his life for his country.

John knew about the upcoming Battle of Tarawa and other intelligence information, more than anyone else on the vessel, which is why he chose to go down with the Sculpin, along with eleven others. Of the forty-two survivors of the vessel, twenty-one would survive, and John was nominated for the Medal of Honor. On the 24th of April 1946, his posthumous Medal of Honor was presented to his wife Margaret and their son John Jr, in a ceremony in San Francisco, California. John Philip Cromwell was 42 years old when he died, and his remains were never recovered. There is a cenotaph for him in the Henry Cemetery in Henry, Illinois, as well as his name being listed on the Courts of the Missing at the Honolulu Memorial in Hawaii.