For conspicuous gallantry and intrepidity at the risk of his life above and beyond the call of duty while serving as chaplain on board the U.S.S. Franklin when that vessel was fiercely attacked by enemy Japanese aircraft during offensive operations near Kobe, Japan, on 19 March 1945. A valiant and forceful leader, calmly braving the perilous barriers of flame and twisted metal to aid his men and his ship, Lt. Commander O'Callahan groped his way through smoke-filled corridors to the open flight deck and into the midst of violently exploding bombs, shells, rockets, and other armament. With the ship rocked by incessant explosions, with debris and fragments raining down and fires raging in ever-increasing fury, he ministered to the wounded and dying, comforting and encouraging men of all faiths; he organized and led firefighting crews into the blazing inferno on the flight deck; he directed the jettisoning of live ammunition and the flooding of the magazine; he manned a hose to cool hot, armed bombs rolling dangerously on the listing deck, continuing his efforts, despite searing, suffocating smoke which forced men to fall back gasping and imperiled others who replaced them. Serving with courage, fortitude, and deep spiritual strength, Lt. Commander O'Callahan inspired the gallant officers and men of the Franklin to fight heroically and with profound faith in the face of almost certain death and to return their stricken ship to port.