Britannica Educational Publishing 
War at Sea and in the Air [PDF ebook] 

Although conflict was once restricted to land, the introduction of warships and planes eventually expanded the theater of war to include both water and sky. New combat strategies emerged with these changing technologies and dramatically impacted such events as the First World War. This comprehensive volume examines the various crafts that have shifted the front lines of war to previously unimagined heights and depths and the tactics that have accompanied these developments.