World War, 1914-1918 38 History 22 Campaigns 9 World War, 1939-1945 6 Aerial operations 5 Pictorial works 4 Naval art and science 3 Naval history, Modern 3 1939-1945 2 Airplanes, Military 2 Biography 2 Causes 2 Chemical warfare 2 Diplomatic history 2 Foreign relations 2 Germany 2 Great Britain 2 Juvenile literature 2 Naval operations 2 Sea-power 2 Social aspects 2 Soldiers 2 Somme, 2nd Battle of the, France, 1918 2 Sources 2 Tanks (Military science) 2 United States 2 World War 2 World War I 2 20th century 1 Aerial operations, American 1