In his ten combat patrols, five in Wahoo and five commanding Tang, O'Kane participated in more successful attacks on Japanese shipping than any other submarine officer during the war.

Morton established a record as an excellent tactician, as he preferred to run the demanding analysis and plots while his executive officer manned the periscopes, a reversal of standard practices.

Under O'Kane, Tang also performed "lifeguard duty", a common joint operation, with a Fast Carrier Task Force, of positioning one or more submarines in a "ditching station" off an enemy island under air attack in order to rescue downed pilots.

O'Kane was captured by the Japanese when Tang was sunk in the Formosa Strait by her own flawed torpedo (a circular run of a Mark 18) during a surface night attack on October 24–25, 1944.

O'Kane lost all but eight members of his crew, and was at first secretly held captive at the Ōfuna navy detention center, then later moved to the regular army Omori POW camp.

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 the commanding officer.

In addition to the Medal of Honor, O'Kane received three Navy Crosses, three Silver Stars, the Legion of Merit with "V" device for valor, the Purple Heart and several other decorations throughout his career.

Boldly maneuvering on the surface into the midst of a heavily escorted convoy, CMDR O'Kane stood in the fusillade of bullets and shells from all directions to launch smashing hits on 3 tankers, coolly swung his ship to fire at a freighter and, in a split-second decision, shot out of the path of an onrushing transport, missing it by inches.

Boxed in by blazing tankers, a freighter, transport, and several destroyers, he blasted 2 of the targets with his remaining torpedoes and, with pyrotechnics bursting on all sides, cleared the area.

Twenty-four hours later, he again made contact with a heavily escorted convoy steaming to support the Leyte campaign with reinforcements and supplies and with crated planes piled high on each unit.

With ships bearing down from all sides, he charged the enemy at high speed, exploding the tanker in a burst of flame, smashing the transport dead in the water, and blasting the destroyer with a mighty roar which rocked the Tang from stem to stern.