French shipbuilder DCNS has taken the wraps off a new concept submarine that combines conventional power with a nuclear-powered attack submarine design.

The vessel, named the long SMX-Ocean, was unveiled at the Euronaval 2014 exhibition in Paris. It would be 328 feet long, displace more than 4,000 tons, dive deeper than 1,000 feet and have a submerged speed of 20 knots.

"This innovative concept ship promises submerged endurance and deployment capabilities that are unprecedented for a conventional-propulsion submarine," DCNS said.

"To achieve this level of performance, DCNS teams have developed and combined a number of innovations, including a high-performance air-independent propulsion system using second-generation fuel cells for submerged endurance of up to three weeks."

DCNS said the submarine features the hull design and general layout of Barracuda-class nuclear submarines, which will enter service with the French Navy in 2017. The combat system, provisions for special forces' missions and masts would be the same.

The SMX-Ocean would carry torpedoes, mines, anti-ship missiles, cruise missiles and their vertical launchers and anti-air missiles.