- Ouvrage Lembach
- Ouvrage Les Aittes
- Ouvrage Les Rochilles
- Ouvrage Les Sarts
- Ouvrage Mauvais-Bois
- Ouvrage Michelsberg
- Ouvrage Molvange
- Ouvrage Mont Agel
- Ouvrage Mont des Welches
- Ouvrage Monte Grosso
- Ouvrage Mottenberg
- Ouvrage Métrich
- Ouvrage Oberheid
- Ouvrage Otterbiel
- Ouvrage Pas du Roc
- Ouvrage Plan Caval
- Ouvrage Plate Lombard
- Ouvrage Restefond
- Ouvrage Rimplas
- Ouvrage Roche-la-Croix
- Ouvrage Rochonvillers
- Ouvrage Rohrbach
- Ouvrage Roquebrune
- Ouvrage Saint-Antoine
- Ouvrage Saint-Gobain
- Ouvrage Saint-Roch
- Ouvrage Saint Ours Bas
- Ouvrage Saint Ours Haut
- Ouvrage Saint Ours Nord-est
- Ouvrage Sainte-Agnès
- Ouvrage Sapey
- Ouvrage Schiesseck
- Ouvrage Schoenenbourg
- Ouvrage Sentzich
- Ouvrage Simserhof
- Ouvrage Soetrich
- Ouvrage Thonnelle
- Ouvrage Téting
- Ouvrage Valdeblore
- Ouvrage Village Coume
- Ouvrage Vélosnes
- Ouvrage Welschhof
- Ouvry Lindfield Roberts
- Ova A. Kelley
- Ovation
- Ovda Airport
- Ove Gjedde
- Over-the-beach capability
- Over-the-horizon Airborne Sensor Information System
- Over in Hero-Land
- Over the Hills and Far Away (traditional song)
- Over the Top: Military March
- Over the Top (1917 song)
- Over the Top (Song)
- Over the Top (painting)
- Over the Top to Victory
- Overall
- Overall length
- Overland Campaign
- Overland Relief Expedition
- Overland train
- Overloon War Museum
- Overmountain Men
- Overpressure (CBRN protection)
- Overseas Internal Security Program
- Overseas Medal
- Overseas Service Bar
- Overseas Service Chevron
- Overseas Service Ribbon
- Overseas Territories Police Medal
- Overseas Tour Extension Incentive Program
- Overseas housing allowance (United States military)
- Overseas interventions of the United States
- Overseas military bases of France
- Overseas military bases of the United Kingdom
- Oversight of United States covert operations
- Oversize cargo
- Overthrow of the Kingdom of Hawaii
- Overthrow of the Roman monarchy
- Overton Brooks
- Overton James
- Overton Keightley
- Overview of 21st-century propaganda
- Overview of 21st century propaganda
- Overwatch
- Overwatch (military tactic)
- Overwatch Battle Group (West)
- Ovesholm Castle
- Oveta Culp Hobby
- Ovezmurat Dykma-Serdar
- Ovid R. Sellers
- Ovida
- Ovila Cayer
- Ovillers-la-Boisselle
- Ovinius Camillus
- Ovius and Novius Calavius
- Ovče Pole Offensive
- Owain Glyndŵr
- Owain ap Cadwgan
- Owain ap Caradog
- Owain mab Urien
- Owasco-class cutter
- Owe Wiktorin
- Owen Aspinall
- Owen Baldwin
- Owen Biddle, Sr.
- Owen Cleary
- Owen Connelly
- Owen Corrie
- Owen Coxe
- Owen D. Young (U.S. Navy)
- Owen Edward Pennefather Lloyd
- Owen Frampton
- Owen Frederick Morton Tudor
- Owen Garriott
- Owen Gun
- Owen Hardy
- Owen Honors
- Owen J. Baggett
- Owen Jones (American politician)
- Owen Jones (congressman)
- Owen K. Garriott
- Owen Lanyon
- Owen Lewis Cope Williams
- Owen Lloyd George, 3rd Earl Lloyd-George of Dwyfor
- Owen M. Begley
- Owen M. Panner
- Owen MacEoin Dubh MacAlister
- Owen Magee
- Owen McIntosh Burns
- Owen Mead
- Owen Morshead
- Owen Phillips (general)
- Owen Roberts (aviator)
- Owen Roe O'Neill
- Owen Rowe
- Owen Rutter
- Owen Scholte
- Owen Southwell
- Owen Stanley
- Owen Summers
- Owen Summers, Jr.
- Owen Thomas (politician)
- Owen Thomas Edgar
- Owen Truelove
- Owen Tudor
- Owen Tudor Boyd
- Owen W. Siler
- Owen Wansbrough-Jones
- Owen Weingott
- Owen West
- Owen Woodhouse
- Owen Wynne (British Army officer)
- Owens Valley Indian War
- Owi Airfield
- Owingsville, Kentucky
- Owingsville Air Force Station
- Owj Tazarve
- Owl Goingback
- Owoye Andrew Azazi
- Owsley Stanley
- Owston Ferry Castle
- Ox Emerson
- Ox tongue spear
- Oxford-class research ship
- Oxford Castle
- Oxford Road Commonwealth War Graves Commission Cemetery
- Oxford Tracked Carrier
- Oxford University Air Squadron
- Oxfordshire Militia
- Oxfordshire and Buckinghamshire Light Infantry
- Oxfordshire and Buckinghamshire Light Infantry War Memorial
- Oxfordshire rising of 1596
- Oxgate Admiralty Citadel
- Oxley War Memorial
- Oxnard Air Force Base
- Oxnard Field
- Oxwich Castle
- Oxyathres of Persia
- Oxybeles
- Oxygen Breathing Apparatus
- Oy Insinööritoimisto Ratas
- Oyake Akahachi
- Oyamada Nobushige
- Oyamada clan
- Oyashio-class submarine
- Oyneg Shabbos
- Oyster Wars
- Oystermouth Castle
- Oyumi
- Oz Brigade
- Ozalj Castle
- Ozark Medieval Fortress
- Ozell Sutton
- Ozerne (air base)
- Ozerne Air Base
- Ozires Silva
- Ozolmuiža Manor
- Ozona Air Force Station
- Ozora P. Stearns
- Ozro J. Dodds
- Ozuki Air Field
- Ozur Toti
- Ozzie Cadena
- Ozzie Virgil, Sr.
- Oława Castle
- P-10 radar
- P-120 Malakhit
- P-12 radar
- P-14 radar
- P-15 Termit
- P-15 radar
- P-18 radar
- P-19 radar
- P-20 radar
- P-25 mine
- P-270 Moskit
- P-30 radar
- P-35 radar
- P-38 can opener
- P-3 radar
- P-40 (disambiguation)
- P-40 APPLE mine
- P-40 radar
- P-500 Bazalt
- P-51VLR
- P-5 Pyatyorka
- P-64 (pistol)
- P-64 Pistol
- P-700 Granit
- P-70 Ametist
- P-70 radar
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