The Russo-Japanese War and particularly the Battle of Tsushima in 1905 was the first test of the new concepts, resulting in a stunning Japanese victory and the destruction of most Russian ships. With the advent of the steamship, it became possible to create massive gun platforms and to provide them with heavy armor protection. The Dreadnought battleships and their successors were the first capital ships that combined technology and firepower with a mobile platform. However, in the first half of the 20th century, the utility of air power in support of the fleet began to emerge. World War I pitted the old Royal Navy against the new Kaiserliche Marine  of Imperial Germany, culminating in the 1916 Battle of Jutland. The future was heralded when the seaplane carrier HMS Engadine and her Short 184 seaplanes joined the battle. In the Black Sea, Russian seaplanes flying from a fleet of converted carriers interdicted Turkish maritime supply routes, Allied air patrols began to counter German U-Boat activity in Britain's coastal waters, and a British Short 184 carried out the first successful torpedo attack on a ship. In 1918 the Royal Navy converted an Italian liner to create the first aircraft carrier, HMS Argus, and shortly after the war the first purpose-built carrier, HMS Hermes was launched. Many nations agreed to the Washington Naval Treaty and scrapped many of their battleships and cruisers while still in the shipyards, but the growing tensions of the 1930s restarted the building programs, with even larger ships. The Yamato-class battleships, the largest ever, displaced 72,000 tons and mounted 18.1-inch  guns.
Question: What was the HMS Argus prior to being an aircraft carrier?
Answer: an Italian liner