The subs, which will be battery-powered and carry six guests plus a pilot, will be able to travel up to 300 metres below the surface of the water.

The design of the U-Boat Worx Cruise Sub 7 submarines includes two clear acrylic spheres for three passengers mounted on a rotating platform, which flank the pilot’s station.

Two subs will be carried onboard both Seabourn Venture, which launches in June 2021, as well as the yet-to-be-named sister vessel, due to debut in 2022.

Robin West, vice president of expedition operations for Seabourn, said: “The undersea world is often considered as the last great frontier on Earth, with more than 80% of the underwater realm remaining unmapped, unobserved, and unexplored.

“With these subs, we’re going to take our guests to places that few have ever seen first-hand, leaving them with a perspective on the world around us that is jaw-dropping and will create stories to last a lifetime.”

Excursions in the subs will be offered for an extra charge and operate “multiple” times per day. There will also be optional extras for passengers such as videos shot both inside and outside the submarines.

For extra comfort, the subs will feature seats with embroidered leather upholstery, air conditioning systems, Bluetooth stereo system and champagne chiller.