| | Commander | Warship commands |
 | | T/A/Lt.Cdr. | O'Brien, Cecil Ru-Ru McLarnon, DSC, RNVR | HMS Fritillary (K 199) |
| | A/Lt.Cdr. | O'Brien, William Donough, DSC, RN | HMS Cottesmore (L 78) |
| | | O'Brien, A G, RNR | HMS Strephon (FY 1829) |
| + | Capt. | O'Conor, Rory Chambers, RN | HMS Neptune (20) |
 | | T/Lt. | O'Donoghue, Guy William Patrick, RINR | HMIS Konkan (J 228) |
 |  | Cdr. | O'Kane, Richard Hetherington, USN | USS Tang (306) |
| | T/Lt. | O'Neill, James Frederick Allen, RNZNVR | HMNZS Kiwi (T 102) |
| | Lt. | O'Neill, Frederick Charles, RNR | HMS LST 9 (LST 9) |
| | Lt. | O'Sullivan, David Dennis, RN | HMS Fowey (L 15 / U 15) |
| | | O'Sullivan, P P, RNR | HMS Virginia (FY 031) |
| | T/Skr. | Oakes, John Arthur, RNR | HMS Mary A. Hastie (FY 1935), HMS De La Pole (FY 558) |
| | Lt. | Oakley, John Philip Holroyde, DSC, RN | HMS Otus (N 92), HMS H 34 (N 34), HMS Otway (N 51), HMS Sea Nymph (P 223), HMS Rorqual (N 74) |
| + | Cdr. | Oakley, Jr., Thomas Benjamin, USN | USS Tarpon (175), USS Growler (215) |
| | T/Cdr. | Oakley, Philip John Bowen, RNR | HMS Rame Head (F 34) |
| | Lt. (jg) | Oaks, Leslie Charles, USN | USS Extractor (ARS 15) |
| | Cdr. | Oddie, Eric Roland John, DSO, RN | HMS Narwhal (N 45), HMS Triad (N 53), HMS Indomitable (92) |
| | Capt. | Oexle, Charles William, USN | USS Windham Bay (CVE 92) |
| | A/Ch.Skr. (A/Skr.Lt.) | Offord, Arthur Charles, RNR | HMS Alcmaria (FY 1525), HMS Angele Marie (FY 1708), HMS Pelagos (4.103), HMS MMS 40 (J 540) |
| | | 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) |
| | Cdr. | Ogden, James Robinson, USN | USS Floyds Bay (AVP 40) |
| | Lt.Cdr. | Ogilvy, John Augustus, RN | HMS Loring (K 565) |
| | Lt. | Ogle, John Chaloner, DSC, RN | HMS H 28 (N 28), HMS P 512 (P 512), HMS P 514 (P 514), HMS Vigorous (P 74), HMS Trenchant (P 331) |
| | Lt.Cdr. | Ogle, Ervin Clinton, USN | USS Gillespie (DD 609) |
| | T/Lt. | Ohre, Erling, RNR | HMS Michael Griffiths (FY 567) |
| | 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) |
| | Rear Admiral | Old, Francis Paxton, USN | USS Prairie (AD 15), USS Indiana (BB 58) |
| | Vice Admiral | Oldendorf, Jesse Barrett, USN | USS Decatur (DD 341), USS Houston (i) (CA 30) |
 | | Cdr. | Oldham, George Carmichael, DSC, RAN | HMAS Swan (L 74 / U 74) |
| | A/Ch.Skr. (A/Skr.Lt.) | Oldman, Frank, RNR | HMS Manor (FY 333), HMS Lord Stanhope (FY 163), HMS Asie (FY 370), HMS Romeo (T 10) |
| | T/Lt. | Oldridge, George Henry, RNR | HMS Lady Rosemary (FY 253) |
| | Cdr. | Olds, Hugh Wilson, USN | USS Tippecanoe (AO 21) |
| | A/Skr.Lt. | Olesen, Gunnar Lie, RNR | HMS Viviana (FY 238), HMS Bombardier (T 304) |
| | | Olesen, A L, RNVR | HMS Oak (T 54), HMS BYMS 2279 (J 1079), HMS BYMS 2142 (J 942) |
| | | Olesen, A, RNR | HMS Phineas Beard |
| | T/Skr. | Olgeirsson, Thorarium Einar, RNR | HMS Ebor Wyke (FY 1601) |
| | Lt. | Oliphant, Lawrence Hugh, DSC, RN | HMS Tantalus (P 318) |
| | Capt. (retired) | Oliphant, Henry Gerard Laurence, DSO, RN | HMS Circassia (F 91) |
| | 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), HMCS Port Colborne (K 326) |
| | 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) |
| | A/Lt.Cdr. | Oliver, Roderick Charles, DSC, 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) |
| | A/Skr.Lt. | Oliver, George Henry, RNR | HMS Kingston Crystal (FY 216), HMS Viviana (FY 238), HMS Else Rykens (FY 255) |
| | T/Lt. | Oliver, Robert Ormsby, RNVR | HMS BYMS 2057 (J 857) |
| | T/A/Ch.Skr. (T/A/Skr.Lt.) | Oliver, Lawrence, RNR | HMS Cotsmuir (FY 550), HMS Svana (FY 1707), HMS MMS 277 (J 777) |
| | | Oliver, G McI, RNVR | HMS Polka (T 139) |
| | Capt. | Oliver-Bellasis, Richard, RN | HMS Euryalus (42), HMS Euryalus (42) |
| | T/Lt. | Olivier, Gerard Dacres, RNVR | HMS ML 102 (ML 102), HMS MTB 713 (MTB 713), HMS MTB 684 (MTB 684) |
| | Capt. | Olney, Alfred Clarence, USN | USS Altamaha (ii) (CVE 18) |
| | T/Lt. | Olsberg, Harold, RNR | HMS Beryl (T 34), HMS Satsa (FY 1734) |
| | T/Lt. | Olsen, Gordon Leonard, RANR(S) | HMAS Bowen (J 285) |
| | Lt. | Olsen, Eliot, USN | USS Grayling (209), USS Blackfish (221) |
| | Lt.Cdr. | Olsen, Robert Irving, USN | USS Angler (240) |
| | | Olsen, Albert Royal, USN | USS Hutchins (DD 476) |
| + | | Olsen, A L, RNON | HNoMS Nordhav II (FY 1906) |
| | Capt. | Olsen, Clarence Edward, USN | USS Worden (DD 352), USS Baltimore (CA 68) |
| | Cdr. | Olsen, Jens G., USNR | USS Victoria (AO 46), USS Marias (AO 57) |
| | T/Lt. | Olsen, Harold Olaf, RNR | HMS William Scoresby (J 122), HMS Thirlmere (FY 206) |
| | T/Lt. | Olsen, Sigvard Haakon, RNR | HMS Gunner (FY 568), HMS Cape Barracouta (4.122), HMS Bouvet 3 (FY 1698) |
| | | Olsen, A J, RNR | HMS Sukha (FY 1767) |
| | T/Lt. | Olsen, Alrid Hancke, RNR | HMS Bouvet 3 (FY 1698) |
| | T/A/Lt.Cdr. | Onslow, Denzil Richard Cranley, RNR | HMS Poppy (K 213), HMS LST 364 (LST 364), HMS LST 415 (LST 415), HMS LST 3020 (LST 3020) |
| + | 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), HMS Grenville (ii) (R 97) |
| | Cdr. | Oom, Karl Eric, OBE, RAN | HMS Gleaner (J 83), HMAS Whyalla (J 153), HMAS Shepparton (J 248) |
| | luitenant ter zee 1e klasse (Lt.Cdr.) | Oorde Van, Hendrik Anthonius, RNN | HNMS Gruno (F 81), HNMS Soemba (T 199) |
| | Cdr. | Opie, III, John Newton, USN | USS Roe (DD 418), USS Bache (DD 470) |
| | Lcmdr | Opp, Clayton Magnus, USCG | USS Gallup (PF-47) |
| | Capt. | Oram, Harry Percy Kendall, RN | HMS Cairo (D 87), HMS Hawkins (D 86) |
| | | Organ, C G, RNVR | HMS ML 117 (ML 117) |
| | Lt. | Orleck, Joseph, USN | USS Nauset (AT 89) |
| | T/Skr. | Ormerod, Joe, RNR | HMS George Robb (FY 685) |
| | Cdr. | Ormsby, Gerald Anthony Gore, DSO, RN | HMS Vanquisher (D 54), HMS Pheasant (U 49), HMS Taff (K 637) |
| | T/Lt. | Ormsby, Edward Oswald, RCNVR | HMCS Digby (J 267) |
| | Skr. | Ornsby, John Twaddle, RNR | HMS Fort Robert (FY 762), HMS Caswell (FY 500), HMS Patti (4.10280) |
| | Capt. | Orpen, Arthur Frederick St. George, DSC, RN | HMS Gannet (T 08), HMS Wanderer (D 74), HMS Hesperus (H 57) |
| | T/Lt. | Orr, George McCraney, RCNVR | HMCS Calgary (K 231) |
| | Cdr. | Orr, Ellis Burton, USN | USS Lancetfish (296) |
| | T/A/Lt.Cdr. | Orr, Douglas Blair, RNVR | HMS Orpheus (FY 1780), HMS Greenfly (FY 156), HMS LST 402 (LST 402) |
| | T/Lt. | Orr, Robert William, RNR | HMS BYMS 2060 (J 860) |
| | Capt. | Orr-Ewing, David, DSO, RN | HMS Diomede (D 92), HMS Abdiel (M 39) |
| + | luitenant ter zee 1e klasse (Lt.Cdr.) | Ort, Johan Willem, RNN | HNMS O 12, HNMS O 22 (P 22) |
| | | Orton, R A, RNVR | HMS ML 913 (ML 913) |
| | Capt. | Osborn, Jr., Donald Roderick, USN | USS Duluth (CL 87) |
| | Lcmdr | Osborn, Philip Ransom, USN | USS Borie (i) (DD 215) |
| | A/Lt.Cdr. | Osborne, Frederick Meares, DSC, RANVR | HMS Gentian (K 90), HMS Vanquisher (D 54), HMS Peacock (U 96) |
| | Lcmdr | Osborne, Edward M, USCGR | USS Forsyth (PF-102) |
| | T/Skr. | Osborne, Arthur, RNR | HMS St. Melante (FY 753), HMS Fazenta (FY 587) |
| | Skr. | Osborne, Arthur Charles Albert, RNR | HMS George D. Irvin |
| | | Osborne, I M, RNVR | HMS SGB 9 / Grey Goose (S 309) |
| | Ens | Osburn, Jr., R. G., USN | USS Holly (AN 19) |
| | Cdr. | Oseth, John Marcus, USN | USS Balch (DD 363) |
| | Cdr. | Osler, Paul Gordon, USN | USS Edwards (ii) (DD 619), USS Harlan R. Dickson (DD 708) |
| | Lt.Cdr. | Ostrander, A. T., USN | USS Preserver (ARS 8) |
| | Lt.Cdr. | Oswald, Adolph Henry, USN | USS Kearny (DD 432) |
| | T/Lt. | Otley, Thomas Sellers, RNVR | HMS Dunraven Castle (FY 570), HMS Sandringham (FY 598), HMS Skudd 5 (FY 1806), HMS Glen Kidston (4.77), HMS Vallay (T 434) |
| | Capt. | Otway-Ruthven, Robert Jocelyn Oliver, DSO, RN | HMS Prince of Wales (53), HMS Flamingo (L 18 / U 18), HMS Glasgow (21), HMS Leander (75) |
| | Lt.Cdr. | Outerbridge, William Woodward, USN | USS Ward (DD 139), USS O'Brien (ii) (DD 725) |
| | Cdr. | Outerson, William, USN | USS Beatty (DD 640), USS Charles P. Cecil (DD 835) |
| | Lt.Cdr. | Ouvry, Aymé Arthur Carrington, DSC, RN | HMS Mastiff (T 10), HMS Westminster (L 40) |
| | T/Lt. | Ovenden, Hedley Allen, RCNR | HMCS Chambly (K 116) |
| | Captain | Overesch, Harvey Edward, USN | USS San Francisco (CA 38) |
| | Lt.Cdr. | Overton, William Arthur, USNR | USS Catfish (339) |
| | | Ovrom, Robert Johnston, USN | USS Epping Forrest (LSD 4) |
| | A/Lt.Cdr. | Owen, Charles Alexander Headon, DSC, RN | HMS Burnham (H 82), HMS Wells (I 95), HMS Stevenstone (L 16) |
| | T/A/Lt.Cdr. | Owen, George Ewart Vaughan, RANR(S) | HMAS Mildura (J 207) |
| | Cdr. | Owen, Hilfort Craft, USN | USS Unimak (AVP 31) |
| | T/Lt. | Owen, David Leslie, RNVR | HMS Fentonian (FY 868), HMS MMS 26 (J 526) |
| | | Owen, H, RN | HMS Migrante (FY 019) |
| + | Cmdr | Owens, Seymour Dunlop, USN | USS Norman Scott (DD 690) |
| | T/Skr. | Owens, John Charles Ernest, RNR | HMS Commander Nasmith (FY 556) |
| | Cmdr | Owens, Hinton Allen, USN | USS Luce (DD 522) |
| | Cdr. (retired) | Owles, Garth Henry Fyson, DSO, DSC, RN | HMS LST 215 (LST 215) |
| | T/Skr. | Owston, Matthew Edward, RNR | HMS Kingston Coral (FY 215) |
| | T/A/Ch.Skr. | Oxborough, Edward Ward, RNR | HMS Milford Countess (FY 564) |
| + | Lt. | Oxborrow, Charles Ernest, DSC, RN | HMS H 50 (N 50), HMS Unshaken (P 54) |
| | T/Lt.Cdr. | O\'Brien, John Barry, RCNVR | HMCS Snowberry (K 166), HMCS Snowberry (K 166), HMCS Long Branch (K 487) |
| | 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) |
| | Lt.Cdr. | O\'Gorman, Theodore A., USNR | USS Muir (DE 770) |
| | T/Lt. | O\'Kelly, Edward Ross, 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), USS Arkansas (BB 33) |
| | Lcmdr | O`Connell, Jr., George Albert, USN | USS Hambleton (DD 455) |
| | Capt. (retired) | O’Connell, Donal Bernard, RN | HMS Resource (F 79) |
| | Capt. | O’Donnell, George Eric Maxia, DSO, RN | HMS Enterprise (D 52), HMS Capetown (D 88), HMS Enterprise (D 52), HMS Malaya (01), HMS Valiant (02) |
