
No superyacht is complete without a mini-submarine that costs a small fortune.

The latest must-have for billionaire yacht owners – the Triton 6600/2 – allows them to explore shipwrecks or other spots at new depths thanks to a revolutionary new passenger compartment that remains at surface pressure even while diving more than a mile beneath the sea.

Priced from $5.5million (£3.8million), the personal submarine has the thickest transparent acrylic hull ever made, providing a spectacular view of marine life at a depth of up to 6,600ft.

Triton 6600/2, a two-person submersible, remains at surface pressure while diving a mile beneath the sea thanks to its acrylic hull

Built by Triton Submarines, the air-conditioned 6600/2 model is billed as the world’s deepest diving submersible with an acrylic hull

Personal submarines allow yacht owners to explore shipwrecks or others spots for pleasure or research (pictured: Triton 3300/3 model)

Built by Triton Submarines, based in Vero Beach, Florida, the two-seater is billed as the world’s deepest diving submersible with an acrylic hull.

With a top speed of nearly 3.5mph (three knots), it takes about an hour for the pilot and a passenger to reach the sub’s maximum depth while they explore the sea for pleasure or research.

Triton 6600/2 has a maximum dive time of 10 hours, although its life support system, with an emergency oxygen supply, lasts 96 hours.

With air conditioning and high-output LED lights, the submarine weighs 14,300lbs and is 13ft long, nearly 11ft wide and nearly 7ft tall.

With a top speed of nearly 3.5mph (three knots), it takes about an hour for the pilot and a passenger to reach the sub’s maximum depth

Triton's earlier 3300/3 model (pictured on a research mission) transported Sir David Attenborough to deep parts of the Great Barrier Reef

Triton CEO Bruce Jones unveiled plans for the new model at the Fort Lauderdale International Boat Show last November.

He said at the time: 'Like other Tritons, the transparent pressure hull provides remarkable viewing and the capability of diving over a mile deep adds tremendous versatility.'

Project manager Ron Stamm added: 'It should take about an hour for the sub to get down to its maximum depth, but once there, the pilot and passenger will have plenty of time to investigate a wreck or some other artifact on the bottom, and shoot video if desired.

'Six 20,000-lumens lights will be standard, but owners will be able to add more if needed to support their video operations.'

Triton 6600/2 is currently available for order and takes about 18 months for delivery.

The company's submersibles are a favourite of superyacht owners and researchers.