Down by the dockside: Take a look around the Navy's latest submarine
Royal Navy submarines patrol the seas for months at a time, providing a key part of the UK's armed defence.
The fleet is being updated with seven new vessels. The Ministry of Defence says the Astute class has greater firepower, better communication equipment and will be harder to detect than its predecessor.
Breakfast's Tim Muffett has been to Barrow-in-Furness where they are being built.