The Oyster has been undergoing sea trials at the European Marine Energy Centre (EMEC) in Orkney since November.
The first two boats, HMS Astute and Ambush, are currently undergoing sea trials.
The 120ft state-of-the-art boat, unveiled by the Queen earlier this month, left Dartmouth three days ago for sea trials.
That's looking more precarious than when it was signed, as the aircraft carrier contract heads towards sea trials in 2017.
The sixth, Duncan, left BAE System's Scotstoun yard on the Clyde on Monday for Portsmouth where it will undergo sea trials.
And as a reward for your endurance, they gave you the gift of Sea Trials. (Laughter.) But you survived.
Testing and specification work is done, and sea trials are underway now.
Full sea trials of the new lifeboat will be held later this year and the first operational craft will be ready in 2013.
The vessel, described as a new generation of warship, is to start 18 months of sea trials before being put into service in 2009.
BBC: NEWS | UK | Scotland | Glasgow and West | HMS Daring sets sail for trials
It emerged last month that Astute had encountered several problems during its sea trials, including leaks and electrical switchboards which were were found to be fitted incorrectly.
The catamaran, which is the size of the centre court at Wimbledon, was unveiled by the Queen in March but suffered a series of accidents during sea trials.
One Royal Navy captain after another would champion his new command's inaugural performance at sea trials, or praise the yard to the hilt when a vessel returned to the port of its birth.
According to recent news reports, Russia is seeking to begin deploying a new class of ballistic missile submarines and their Bulava missiles before the end of 2012, preceded by sea trials of both.
This year, China has passed several milestones in developing military technology that could be used in these areas: It conducted the first test flight of a stealth fighter prototype in January and began sea trials of its first aircraft carrier in August.
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