HMS Campania was a seaplane tender and aircraft carrier, converted from an elderly ocean liner by the Royal Navy early in the First World War. After her conversion was completed in mid-1915 the ship spent her time conducting trials and exercises with the Grand Fleet. These revealed the need for a longer flight deck to allow larger aircraft to take off, and she was modified accordingly. Campania missed the Battle of Jutland in May 1916, but made a number of patrols with elements of the Grand Fleet. She never saw combat and was soon relegated to a training role because of her elderly machinery. In November 1918 Campania was anchored with the capital ships of the Grand Fleet when a sudden storm caused her anchor to drag. With no second anchor being laid, she hit several of the ships and the collisions punctured her hull; she slowly sank, with no loss of life.

A seaplane tender is a boat or ship that supports the operation of seaplanes. Some of these vessels, known as seaplane carriers, could not only carry seaplanes but also provided all the facilities needed for their operation; these ships are regarded by some as the first aircraft carriers and appeared just before the First World War.