The British SSBN Vanguard is, after 14 years of service, taking a 42 month break to get a $422 million refurbishment. This will include installation of new reactor, similar to the one used on the new Astute SSN. This new reactor design eliminates the expensive refueling process (by doubling the amount of fuel installed initially). The refurb will improve crew quarters and safety systems, along with the usual upgrades to electronics and mechanical equipment. This refurb is expected to keep the Vanguard going for at least twenty more years.
The four Vanguard class boats are large (14,000 tons surface displacement, 465 feet long, crew of 135), and entered service in the 1990s. They carry 16 Trident II missiles, weighing 59 tons, with a range of 11,300 kilometers and each carrying up to eight warheads.