How to Build a Nuclear Submarine
The submarines, which cost more than £1bn, take years to design and build, with the first of class taking 14 years to complete. More than a year of the top secret process at one of the most secure places in the country - the BAE Systems shipyard in Cumbria - has been captured on camera.
Weighing 7,000 tons and measuring 100 metres in length, assembling the different sections is a delicate business.
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