UK nuclear propelled attack submarine (SSN) HMS Tireless probably at Her Majesty's Naval Base (HMNB) Clyde in Scotland.
HMS Tireless inside. No VLS - its Tomahawks are launched from its horizontal torpedo tubes.
Australia's news.com.au, April 2, 2014, reports http://www.news.com.au/travel/travel-updates/nuclear-submarine-joins-search-for-missing-malaysia-airlines-flight-mh370/story-fnizu68q-1226871783527
http://en.wikipedia.org/wiki/HMS_Tireless_(S88) was launched in 1984 and has a mixed safety record. Tireless will probably attempt to detect “pings” emitted by MH370's Black Box using its passive sonars and other electronic receivers. It is less likely that Tireless' active sonars and other sensors would be able to "shape" (detect) MH370 debris floating or on the ocean floor. Tireless is unlikely to be equipped to recover MH370 debries from the ocean floor.
HMS Echo - a multi-role hydrographic survey ship of 3,500 tons is likely to be more useful in search and recovery.