Since the 1980s, Swedish surface warships have been named after Swedish cities, while submarines are named after Swedish provinces and minehunters after Swedish lighthouses. The surface ships are mostly small, relying on agility and flexibility. Examples of these are the "Stockholm" and "Göteborg"-class corvettes. The Navy is currently taking into service the new, larger, of stealth corvettes. A new submarine class, , similar to the older , was commissioned in 1998. Its air-independent Stirling engine enables submerged endurance never before seen in conventional submarines. "Gotland" has been on lease with crew and all to the US Navy and was based in San Diego.