Two 'milestone' submarines have been unveiled, vessels that according to the maker can be transformed into underwater casinos, wedding and private dining venues and configured for cocktail parties.

Florida-based Marine engineering firm Triton Submarines said it 'threw out the rule book' when it came to designing its new first-of-their-kind Triton 660/9 and 660/7 AVA submarines.

The result is a twin set of submarines capable of reaching depths as great as 200m (660ft) that each come with a 3.6-metre- (12ft) wide interior space that 'feels like a regular room rather than a submersible' and can be reconfigured for all sorts of entertainment experiences.

The ultra-large interior can be equipped with generous seating, integrated lighting, a high-fidelity surround audio system and air-conditioning.

What's more, AVA's pilot has full visibility and sits in the centre of the passengers, allowing everyone on board to see the same thing.

This allows the pilot to curate the dive and act as a guide as well, narrating the experience for those on board, Triton says, adding: 'Activities are limited only by the owner's imagination.'

The secret behind the submarines' unprecedented space is their 'world-first free-form acrylic hulls'.

Triton says: 'As the shape remains constant across its width, so much more of the space is realised as additional headroom, legroom and usable space.'

Triton's principal designer, John Ramsay, explained: 'With the free-form acrylic geometry we were able to finely adjust the submersible's pressure hull to perfectly suit the interior space and external body shape of the vehicle. By departing from the traditional constraints of a sphere or cylinder we were able to make minute refinements to the profile, optimising the use of every millimetre.