World War, 1939-1945 1,583 History 690 Campaigns 612 World War, 1914-1918 243 Biography 220 World war, 1939-1945 175 Aerial operations 133 World War 112 Naval operations 106 Regimental histories 75 Foreign relations 69 Secret service 68 Aerial operations, British 64 Personal narratives 59 Tank warfare 58 Germany 56 Airplanes, Military 53 Equipment and supplies 52 History, Military 52 Personal narratives, British 51 Juvenile literature 50 Submarine 50 Causes 47 Naval operations, American 45 Personal narratives, American 43 Great Britain 42 United States 41 Pictorial works 40 Soldiers 40 Aerial operations, American 38