History World War, 1914-1918 Campaigns 13 World War, 1939-1945 12 Naval operations 7 20th century 5 Great Britain 5 Aerial operations 4 Germany 4 Psychological aspects 4 Air warfare 3 Military planning 3 Military policy 3 Regimental histories 3 Social aspects 3 Submarine 3 Airplanes, Military 2 Battles 2 Design and construction 2 Equipment and supplies 2 Militarism 2 Military history, Modern 2 Peace 2 Pictorial works 2 Revolutions 2 Shipwrecks 2 Strategy 2 Tank warfare 2 War 2 War and society 2