The fifth Astute-class attack submarine being built for the Royal Navy has been launched at BAE Systems' site in Barrow-in-Furness, Cumbria.
HMS Anson, officially named in December, emerged from the Devonshire Dock Hall and entered the water for the first time.
The 7,400-tonne nuclear submarine is the fifth of an eventual fleet of seven Astute-class submarines.
Steve Timms, managing director at BAE Systems' submarines business, said the launch marked "an important milestone in the Astute programme".
"Seeing Anson enter the water at such an advanced state is a tangible demonstration of everyone's hard work over the years," he said.
"Designing and building nuclear-powered submarines is a national endeavour and days like this bring a huge sense of pride for our workforce, our partners in the submarine enterprise and our UK supply chain, not to mention our communities."
HMS Anson will now begin the next phase of its test and commissioning programme before leaving Barrow for sea trials with the Royal Navy next year.
Measuring 97m long, the Astute-class boats are the largest and most advanced attack submarines ever built for the Royal Navy.
They are also the first Royal Navy submarines to be fitted without optical periscopes – instead using high-specification video technology.
The submarines are also capable of circumnavigating the globe submerged and producing their own oxygen and drinking water.
A further two boats are currently under construction.
The launch of HMS Anson was a special moment for the Barrow shipyard, which is celebrating its 150th year.
The first submarine for the Royal Navy was built in Barrow, as well as every other submarine currently in service.