HMS Astute, the Royal Navy's newest and largest nuclear-powered attack submarine, has sailed to begin sea trials. The 7400-tonne sub, which was escorted from Barrow-in-Furness by a large number of tugs and police boats, will carry out initial trials while en route to her new base at Faslane.

Astute is the first in a new class of submarine whose construction has been described as more complex than that of the space shuttle. She will never need to be refuelled, and advanced on-board life support systems mean she can circumnavigate the globe without surfacing.

The 100m-long boat has taken eight years to build and is the first British submarine to be fitted with a new optronics system rather than conventional periscopes.