World War, 1939-1945 Campaigns 441 History 433 Biography 142 Aerial operations 102 Naval operations 80 Aerial operations, British 56 Secret service 56 Regimental histories 52 Tank warfare 50 Personal narratives, British 45 Equipment and supplies 44 Germany 41 Naval operations, American 41 Personal narratives, American 40 Personal narratives 39 History, Military 36 Foreign relations 34 Submarine 33 Aerial operations, American 32 Pictorial works 30 World War, 1914-1918 30 Causes 29 Juvenile literature 29 Great Britain 28 Diplomatic history 27 Military intelligence 27 World war, 1939-1945 25 Airplanes, Military 24 Prisoners of war 24