Four submarines of the Vanguard Class SSBN (Ship Submersible Ballistic Nuclear) provide the United Kingdom with a strategic nuclear deterrent force. The first submarine was launched in 1993 carrying Trident missiles and significantly contributed to the Alliance's deterrent forces.

The submarines were built in specially constructed facilities at Vickers Shipbuilding and Engineering Ltd (now BAE Systems Submarine Solutions), Barrow-in-Furness, Cumbria. They are the largest submarines manufactured in the UK, displacing 15,900 tons submerged.

Wärtsilä solution
Each submarine has Seals & Bearings on the main propulsion drive, designed to very specific operational needs. The design criteria are classified due to the vessel type. However, these products have proven to be extremely reliable in operation.