Thousands of people were at the ceremony at BAE Systems' Devonshire Dock Hall in Barrow to mark the end of the build process for Artful.
Another four of the nuclear-powered submarines are being built at the yard.
The ceremony was carried out by Amanda Lady Zambellas, wife of the Royal Navy's First Sea Lord, Admiral Sir George Zambellas.
BAE Systems Maritime - Submarines managing director John Hudson said: "The design and build of a nuclear-powered submarine is as challenging as it is complex, so today represents a significant milestone in Artful's programme.
"It requires real skill and innovation to deliver submarines as sophisticated as Artful and this would not have been possible without the valued contribution of our employees and the collaborative efforts of the whole submarine enterprise."
Artful will remain at the Barrow yard while commissioning activities are carried out and is due to be launched early next year for further tests.
HMS Astute and HMS Ambush have already been launched. The other vessels are at various stages in the design and build process and will be called Audacious, Anson, Agamemnon and Ajax.
The Barrow yard has been working on the Astute programme since 2001.
The Ministry of Defence said the Astute class of submarines have greater firepower, state-of-the-art communications equipment and advanced stealth technology, making them quiet and harder to detect.

The Japanese firm expects net profit in the year to March of 1.7 trillion yen ($15.1bn; Â£12.1bn), compared with a previous forecast of 1.55 trillion yen.
That is despite losing its top-selling carmaker status to Volkswagen in 2016,
Meanwhile, Toyota said it had begun formal talks to work with Suzuki on projects including safety technology.
Analysts said the partnership - which could also involve collaboration on vehicles that were less damaging to the environment - would give Suzuki access to Toyota's technology. Benefits for Toyota are likely to include tapping in to Suzuki's strong market position in India.
The forecast for 2016-17 profits is still below the 2.1 trillion yen profit it recorded a year earlier.
But with Japan's yen weakening against the dollar, it will benefit from sales overseas which are worth more when converted back into the local currency.
Like other Japanese carmakers, Toyota is watching closely for any trade tariffs introduced by the new US administration.
At the moment, only about half of the cars it sells in the country are manufactured locally. Last month, US President Donald Trump criticised it for making vehicles in Mexico to sell over the border.
The US is its biggest market, and it is struggling to meet demand for bigger vehicles such as sport utility vehicles. Lower petrol prices have made such models more affordable to drive.

Bohn, ranked world number 71, had chest pains following the second round and called for a medic.
"He was taken by ambulance to Palm Beach Gardens Medical Center, where tests revealed a mild heart attack," a PGA Tour statement said.
"Jason is resting comfortably and in good spirits," his agent added.
"He is scheduled to have more tests this weekend," Justin Richmond said.
"We know he appreciates the concern from so many people in the PGA Tour family who have reached out."
The PGA Tour statement added Bohn's wife was at "home in Atlanta but his in-laws joined him at the hospital, as did fellow player George McNeill, who said Bohn was in good spirits".
Bohn carded 72 in the second round, which would have seen him make the cut at the PGA National.
Saturday's third round proceeded without Bohn, and finished with Spain's Sergio Garcia and Australia's Adam Scott sharing a commanding four-shot lead over America's Blayne Barber.
Northern Ireland's Rory McIlroy missed the cut for a second year.
The third Astute Class submarine to be built at a Cumbrian shipyard has been named.
[NEXT_CONCEPT]
Toyota says its full-year profits will be better than expected thanks to a pick-up in sales and a boost from currency fluctuations.
[NEXT_CONCEPT]
American two-time PGA Tour winner Jason Bohn has suffered a heart attack at the age of 42 during the Honda Classic in Florida.