| | Commander | Warship commands |
 | | T/A/Lt.Cdr. | O'Brien, Cecil Ru-Ru McLarnon, DSC, RNVR | HMS Fritillary (K 199) |
 | | | O'Brien, John Barry, RCNVR | HMCS Snowberry (K 166), HMCS Snowberry (K 166), HMCS Long Branch (K 487) |
| | A/Lt.Cdr. | O'Brien, William Donough, DSC, RN | HMS Cottesmore (L 78) |
| | Lt. | O'Sullivan, David Dennis, RN | HMS Fowey (L 15 / U 15) |
| | Lt. | Oakley, John Philip Holroyde, DSC, RN | HMS H 34 (N 34), HMS Sea Nymph (P 223), HMS Rorqual (N 74) |
 | + | Cdr. | Oakley, Jr., Thomas Benjamin, USN | USS Tarpon (175), USS Growler (215) |
| | Cdr. | Oddie, Eric Roland John, DSO, RN | HMS Narwhal (N 45), HMS Triad (N 53) |
| | Capt. | Oexle, Charles William, USN | USS Windham Bay (CVE 92) |
| | | Ofstie, Ralph Andrew, USN | USS Essex (CV 9) |
| | T/A/Cdr. | Ogden, William Greame, DSC, RNVR | HMS Lady Madeleine (FY 283), HMS Allington Castle (K 689) |
| | Capt. | Ogden, Samuel Burr, USN | USS Cascade (AD 16) |
| | | Ogilvy, John Augustus, RN | HMS Loring (K 565) |
| | Lt. | Ogle, John Chaloner, DSC, RN | HMS H 28 (N 28), HMS Vigorous (P 74), HMS Trenchant (P 331) |
| | Lt.Cdr. | Ogle, Elvin Clinton, USN | USS Gillespie (DD 609) |
| | Lt.Cdr. | Olch, Isaiah, USN | USS Stack (DD 406) |
| | T/Lt.Cdr. | Old, Ernest George, RCNR | HMCS The Pas (K 168), HMCS The Pas (K 168), HMCS Loch Alvie (K 428) |
| | Capt. | Oldendorf, Jesse Barrett, USN | USS Decatur (DD 341), USS Houston (i) (CA 30) |
 | | | Oldham, George Carmichael, RAN | HMAS Swan (L 74 / U 74) |
| | Lt. | Oliphant, Lawrence Hugh, DSC, RN | HMS Tantalus (P 318) |
| | A/Cdr. | Oliver, Henry Lewis, RN | HMS Atheling (D 51) |
| | T/A/Lt.Cdr. | Oliver, Maurice Faulkman, RCNR | HMCS Halifax (K 237), HMCS Chebogue (K 317) |
| | Cdr. | Oliver, Percy James, RN | HMS Acasta (H 09), HMS Hecla (i) (F 20) |
| | Rear-Admiral | Oliver, Robert Don, DSC, RN | HMS Devonshire (39), HMS Swiftsure (08) |
| | | Oliver, Roderick Charles, RN | HMS Speedwell (J 87) |
| | Rear-Admiral | Oliver, Geoffrey Nigel, DSO, RN | HMS Hermione (74) |
| | Capt. | Oliver, Frederick Lansing, USN | USS Salt Lake City (CA 25) |
| | | Oliver, Robert John, USN | USS Halford (DD 480) |
| | Capt. | Oliver-Bellasis, Richard, RN | HMS Euryalus (42) |
| | Capt. | Olney, Alfred Clarence, USN | USS Altamaha (ii) (CVE 18) |
| | T/Lt. | Olsen, Gordon Leonard, RANR(S) | HMAS Bowen (J 285) |
| | Lt. | Olsen, Eliot, USN | USS Grayling (209), USS Blackfish (221) |
| | Lt.Cdr. | Olsen, Roger I., USN | USS Angler (240) |
| | | Olsen, Albert Royal, USN | USS Hutchins (DD 476) |
| | Capt. | Olsen, Clarence Edward, USN | USS Worden (DD 352), USS Baltimore (CA 68) |
| + | | Olsen, A L, RNON | HNoMS Nordhav II (FY 1906) |
| | T/A/Lt.Cdr. | Onslow, Denzil Richard Cranley, RNR | HMS Poppy (K 213) |
| + | Capt. | Onslow, Richard Francis John, DSC, RN | HMS Coventry (D 43), HMS Hermes (D 95) |
| | Capt. | Onslow, Richard George, DSO, RN | HMS Ashanti (F 51), HMS Quilliam (G 09) |
| | Cdr. | Oom, Karl Eric, OBE, RAN | HMS Gleaner (J 83), HMAS Whyalla (J 153), HMAS Shepparton (J 248) |
| | | Oorde Van, Hendrik Anthonius, RNN | HNMS Gruno (F 81) |
| | Cdr. | Opie, III, John Newton, USN | USS Roe (DD 418), USS Bache (DD 470) |
| | Capt. | Oram, Harry Percy Kendall, RN | HMS Cairo (D 87), HMS Hawkins (D 86) |
| | Lt. | Orleck, Joseph, USN | USS Nauset (AT 89) |
| | Cdr. | Ormsby, Gerald Anthony Gore, DSO, RN | HMS Vanquisher (D 54), HMS Pheasant (U 49), HMS Taff (K 637) |
| | Capt. | Orpen, Arthur Frederick St. George, DSC, RN | HMS Wanderer (D 74), HMS Hesperus (H 57) |
| | | Orr, G. M., RCNVR | HMCS Calgary (K 231) |
| | Cdr. | Orr, Ellis Burton, USN | USS Lancetfish (296) |
| | Capt. | Orr-Ewing, David, DSO, RN | HMS Hood (51), HMS Diomede (D 92), HMS Abdiel (M 39) |
| + | luitenant ter zee 1e klasse (Lt.Cdr.) | Ort, Johan Willem, RNN | HNMS O 22 (P 22) |
| | Capt. | Osborn, Donald Roderick, USN | USS Duluth (CL 87) |
| | A/Lt.Cdr. | Osborne, Frederick Meares, DSC, RANVR | HMS Gentian (K 90), HMS Vanquisher (D 54), HMS Peacock (U 96) |
| | Cdr. | Oseth, John Marcus, USN | USS Balch (DD 363) |
| | Cdr. | Osler, Paul Gordon, USN | USS Harlan R. Dickson (DD 708) |
| | Lt.Cdr. | Oswald, Adolph Henry, USN | USS Kearny (DD 432) |
| | Capt. | Otway-Ruthven, Robert Jocelyn Oliver, DSO, RN | HMS Flamingo (L 18 / U 18), HMS Leander (75) |
| | Lt.Cdr. | Outerbridge, William Woodward, USN | USS Ward (DD 139), USS O'Brien (ii) (DD 725) |
| | Cdr. | Outerson, William, USN | USS Charles P. Cecil (DD 835) |
| | Lt.Cdr. | Ouvry, Aymé Arthur Carrington, DSC, RN | HMS Mastiff (T 10), HMS Westminster (L 40) |
| | | Ovenden, Hedley Allen, RCNR | HMCS Chambly (K 116) |
| | Lt.Cdr. | Overton, William Arthur, USN | USS Catfish (339) |
| | A/Lt.Cdr. | Owen, Charles Alexander Headon, DSC, RN | HMS Burnham (H 82), HMS Wells (I 95), HMS Stevenstone (L 16) |
| | | Owen, George Ewart Vaughan, RANR(S) | HMAS Mildura (J 207) |
| + | Cdr. | Owens, Seymour Dunlop, USN | USS Norman Scott (DD 690) |
| + | Lt. | Oxborrow, Charles Ernest, DSC, RN | HMS Unshaken (P 54) |
| | Lt.Cdr. | O\'Brien, Timothy Joseph, USN | USS Preston (i) (DD 379) |
| | Lt.Cdr. | O\'Brien, William John, USN | USS Lamberton (DMS 2) |
| | | O\'Connor, L. B., USN | USS Tuscaloosa (CA 37) |
| + | Capt. | O\'Conor, Rory Chambers, RN | HMS Neptune (20) |
| | Lt.Cdr. | O\'Gorman, Theodore A., USNR | USS Muir (DE 770) |
| | Cdr. | O\'Kane, Richard Hetherington, USN | USS Tang (306) |
| | | O\'Kelly, E. R., RCNVR | HMCS Dauphin (K 157) |
| | Lt.Cdr. | O\'Mara, William Leslie, DSC, RN | HMS Rhyl (J 36), HMS Sharpshooter (J 68) |
| | Lt.Cdr. | O\'Neil, Jr., Guy Edward, USN | USS Gunnel (253) |
| | Lt.Cdr. | O\'Rear, George McFadden, USN | USS Smith (DD 378) |
| | | O`Donnell, James B, USNR | |
| | Capt. | O’ Donnell, George Eric Maxia, DSO, RN | HMS Enterprise (D 52), HMS Malaya (01), HMS Valiant (02) |