World War, 1939-1945 Campaigns 378 History 361 Biography 127 Aerial operations 77 Naval operations 67 Secret service 54 Regimental histories 46 Personal narratives, British 45 Aerial operations, British 43 Tank warfare 42 Personal narratives, American 38 Germany 37 History, Military 35 Equipment and supplies 32 Foreign relations 31 Personal narratives 31 Submarine 30 Aerial operations, American 28 Military intelligence 27 Naval operations, American 27 Causes 26 Great Britain 25 World War, 1914-1918 25 Diplomatic history 23 Prisoners of war 23 Soldiers 22 United States 22 Airplanes, Military 21 Prisoners and prisons, Japanese 21