The additional weight of the armour on these first ironclad warships meant that they could have only one gun deck, and they were technically frigates, even though they were more powerful than existing ships-of-the-line and occupied the same strategic role. The phrase 'armoured frigate' remained in use for some time to denote a sail-equipped, broadside-firing type of ironclad. For a time, they were the most powerful type of vessel afloat. Towards the end of the 19th century, the term 'frigate' fell out of use. Armoured vessels were designated as either 'battleships' or 'armoured cruisers', while unarmoured vessels including frigates and sloops were classified as 'unprotected cruisers'. The only surviving screw frigate is the Danish "Jylland". The steam sloop HMS "Gannet " spent many years as a training ship and is now preserved at Chatham. The Dutch steam frigate HNLMS "Bonaire" is currently undergoing restoration as a museum ship. ARA "Uruguay" of the Argentinian navy is the last surviving steam and sail corvette. Japanese frigate Kaiyō Maru was rebuilt as a museum ship in 1990.