HMS Vanguard, the oldest of the UK's Trident nuclear missile submarines, has begun a four year refit at HM Naval Base Devonport.
The submarine was withdrawn from the pool of three submarines available for nuclear-armed patrols at sea and arrived at Devonport at the beginning of December 2015 for the refit.
The submarine will undergo a full refurbishment over the refit period, and will be fitted with a replacement reactor core and new reactor fuel during the refit period as well as upgraded missile launch equipment and computer systems.
Vanguard's last refuelling, completed in 2004 was intended to be the submarine's last. However, in January 2012 radiation was detected in coolant water from a naval test reactor at the Vulcan naval reactor test establishment at Dounreay, leading to concerns about the integrity of the reactors which power Vanguard class submarines. As a result Vanguard is receiving a further unscheduled refit, which will also help extend its life and so it can remain in service until the early 2030s, when the 'Successor Trident replacement submarines are intended to enter service. The submarine is expected to remain at Devonport until 2019, when the refit is scheduled to have been completed.
HMS Vanguard's arrival at Devonport coincided with the departure of fellow Vanguard Class submarine, HMS Vengeance, which left the base a few days later following its own three and a half year, £350 million refit and refuel. Vengeance is currently undertaking Demonstration and Shakedown Operations (DASO) which will culminate in a trap across the Atlantic to reload its arsenal of Trident missiles in the USA and undertake a test firing of an unarmed missile. Following the test the submarine will return to HM Naval Base Clyde to arm its missiles with nuclear warheads, and then re-enter the Trident submarine patrol cycle.