History 28 World War, 1939-1945 15 Airplanes, Military 12 Encyclopedias 10 Pictorial works 8 Equipment and supplies 6 Fighter planes 6 Warships 6 Tanks (Military science) 5 Aerial operations 4 Airplanes 4 Armored vehicles, Military 4 Naval operations 4 Firearms 3 Submarines (Ships) 3 20th century 2 21st century 2 Aeronautics, Commercial 2 Army 2 Artillery 2 Astronomy 2 Bombers 2 Chronology 2 Corvettes (Warship) 2 Destroyers (Warship 2 Frigates 2 Golf 2 Juvenile literature 2 Military 2 Special Air Service 2