He was born in Dover, New Hampshire, graduated from the U.S. Naval Academy in May 1934 and spent his first years of active duty in the cruiser Chester and destroyer Pruitt. He received submarine instruction in 1938 and was then assigned to Argonaut until 1942. Lieutenant O'Kane then joined the precommissioning crew of the new submarine Wahoo, serving as her Executive Officer under Commanding Officer Dudley W. Morton and establishing a record as a very promising tactician.
In July 1943, Lieutenant Commander O'Kane was detached from Wahoo and soon became Prospective Commanding Officer of Tang (SS-306), which was then under construction. He placed her in commission in October 1943 and commanded her through her entire career. In five war patrols, O'Kane and Tang sank an officially recognized total of 24 Japanese ships, establishing one of the Pacific War's top records for submarine achievement. He was captured by the Japanese when his boat was accidently sunk off China during the night of 24-25 October 1944 and was secretly held prisoner until the war's end some ten months later. Following his release, Commander O'Kane was awarded the Medal of Honor for his "conspicuous gallantry and intrepidity" during his submarine's final operations against Japanese shipping.
In the years following World War II, Commander O'Kane served with the Pacific Reserve Fleet as Commanding Officer of the submarine tender Pelias, testified at Japanese war crimes trials, was Executive Officer of the submarine tender Nereus and was Commander Submarine Division 32. He was a student at the Armed Forces Staff College in 1950-51 and was subsequently assigned to the Submarine School at New London, Connecticut, initially as an instructor and, in 1952-53, as Officer in Charge.
Promoted to the rank of Captain in July 1953, O'Kane commanded the submarine tender Sperry until June 1954 and then became Commander Submarine Squadron Seven. Following studies at the Naval War College in 1955-56, he served in Washington, D.C, with the Ship Characteristics Board. Captain O'Kane retired from active duty in July 1957 and, on the basis of his extensive combat awards, was simultaneously advanced to the rank of Rear Admiral on the Retired List.
The guided missile destroyer O'Kane (DDG-77) is named in honor of Rear Admiral O'Kane.