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O

Oak Grove, battle of, 25 June 1862
Oak, HMS (1912)
Oakland, USS (CL-95)
O'Bannon, USS (DD-177)
Obdurate, HMS (1916)
Obedient, HMS (1915)
Oberon, HMS (1916)
Ober-Mörlen, combat of, 9 July 1796
O'Brien Class Destroyers
O'Brien, USS (DD-51)
O'Brien, USS (DD-415)
Observer, HMS (1916)
Ocaña, battle of, 11 November 1809
Ocaña, combat of, 11 November 1809
Ocean, HMS
Ochenskopf, Operation, 26 February – 19 March 1943
Octavia, HMS (1916)
Octodurus, battle of, winter 57/56 B.C.
Odon counterattack, 29 June-1 July 1944
Offa, HMS (1916)
Offheim, combat of, 7 July 1796
O'Hare, Edward “Butch” (1914-1943)
Oitabén River, combat of the, 7-8 June 1809
OKA-38 Aist/ ShS
Okinawa, April-June 1945, I: Preparation
Okinawa, April-June 1945, I: The Battle
Oklahoma, USS (BB 37)
Oklahoma City, USS (CL-91)
Öländ, battle of, 12-13 August 1564
Oldendorf, Rear Admiral Jessie, 1887-1972
Old Fort Wayne, battle of, 22 October 1862
Oliva, peace of, 3 May 1660
Olive, Operation (25 August-October 1944) - First attack on the Gothic Line
Olivenza, siege of, 11-22 January 1811
Olivenza, siege of, 9 April-15 April 1811
Olpae, battle, 426
Olynthus, battle of, 382 BC
Olynthus, battle of, 381 BC
Olynthus, siege of, early 479 BC
Olynthus, siege of, 348 BC
Omaha Beach, 6 June 1945
Omaha Class Cruisers
Omaha, USS (CL-4)
Onager
Oneglia, combat of, 7 May 1800
Onomarchus, d.353 B
Onslaught, HMS (1915)
Onslow, HMS (1916)
Opal, HMS (1915)
Open Intelligence
Operation Moses (Israel/Ethiopia 1980's)
Operation Thunderbolt (Entebbe Raid), 3rd/4th July 1976
Ophelia, HMS (1915)
Opi
Oporto, battle of, 29 March 1809
Oporto, battle of, 12 May 1809
Opossum, HMS (1895)
Orchard Knob, battle of, 23 November 1863
Orchomenus, battle of, c.352 BC
Orchomenus, battle of, 86 B.C.
Orchomenos, siege of, 418 BC
Ordnance, 7.2in Howitzer Mk I-V
Ordnance, 7.2in Howitzer Mk 6
Ordnance, BL 2.75in mountain gun
Ordnance, BL 5-in field howitzer
Ordnance, BLC 15-pounder field gun
Ordnance, jointed BL 10-pounder mountain gun
Ordnance, QF 2.95in mountain gun (pack howitzer)
Ordnance, QF 3.7in mountain or pack howitzer
Ordnance, QF 4.5in field howitzer
Ordnance, QF 15-pounder Ehrhardt (QF 15-pounder Mark I)
Ordnance QF 18-pounder field gun Mk I
Ordnance QF 18-pounder field gun Mk IV
Ordronaux, USS (DD-617)
Oregon City, USS (CA-122)
Orgetorix, d.61-60 BC
Orion class battleships
Orkhan, son of Othman, early Ottoman ruler (1326-1361) Orlau-Frankenau, battle of, 24 August 1914 (East Prussia)
Orleans, siege of, September 1428 to May 1429
Orleans, siege of, 4 February-March 1563
Ortona, battle of, 20-27 December 1943
Orwell, HMS (1898)
Oslo, German attack on, 9 April 1940
Ormonde, James Butler, second duke of, 1665-1745
Orontes, battle of the, 28 June 1098 (First Crusade)
Oropesa, siege of, 19 September-11 October 1811
Osborne, USS (DD-295)
Osmond Ingram, USS (DD-255/ AVD-9/ APD-35)
Ospedaletto, combat of, 11 April 1809
Osprey, Hawker
Osprey, HMS (1897)
Ostermann-Tolstoy, Alexander Ivanovich, 1771-1857
Ostrich, HMS (1900)
Ostrolenka, combat of, 16 February 1807
Ostrovno, battle of, 25-26 July 1812
Ostwind I/ Flakpanzer IV/3.7cm FlaK
Ostwind II/ Flakpanzer IV/ 3.7cm Flakzwilling
Oswiu, king of Bernicia and Northumbria, (d.670)
OT-26 Flamethrower Tank
OT-34 Flamethrower Tank
OT-130 Flamethrower Tank
OT-133 Flamethrower Tank
OT-134 Flamethrower Tank
Othman, founder of Ottoman power (ruled 1289-1326)
Ott, Karl Peter, Freiherr von Bartokez, 1738-1809
Otter, HMS (1896)
Otter Light Reconnaissance Car (Canada)
Otterburn, battle of, 5 August 1388
Ouche, battle of the, 500
Oudenaarde, battle of, 11 July 1708 (Belgium)
Oudinot, Nicolas Charles, Duc De Reggio 1767-1847.
Ourcq River, battle of the, 5-9 September 1914
Ourthe, battle of the, 18 September 1794
Ouse, HMS (1905)
Outram, General Sir James (1803-63)
Overland Campaign against Richmond, 1864
Overlord, Operation / Battle of Normandy (6 June to 25 August 1944)
Owl, HMS (1913)
Overton, USS (DD-239/ APD-23)
Ozawa, Vice Admiral Jisaburo, 1886-1966