World War, 1939-1945 Campaigns 227 History 214 Biography 70 Aerial operations 67 Naval operations 49 Equipment and supplies 29 Secret service 28 Aerial operations, British 27 Tank warfare 27 Naval operations, American 26 Personal narratives 23 Personal narratives, American 23 Germany 20 Personal narratives, British 20 Juvenile literature 19 Regimental histories 18 Pictorial works 17 Submarine 17 History, Military 15 Naval operations, British 15 Aerial operations, American 14 Great Britain 14 United States 14 World War, 1914-1918 14 Airplanes, Military 13 Armed Forces 13 Foreign relations 13 Military intelligence 13 Atrocities 12