Billionaires at the Monaco Yacht Show last week found a new plaything to keep them occupied, the DeepFlight Super Falcon underwater aeroplane.
Red Bull founder Dietrich Mateschitz bought one last month at a cool $1.7m and now joins venture capitalist Thomas Perkins, once the owner of the world's biggest yacht.
London's Graham Hawkes, designer of the submersibles, even had one of his designs featured in James Bond film 'For Your Eyes Only.'
Hawkes originally built what he describes as "normal" submersibles for the oil and gas industry, and for the military, before realising that he could develop the technology to fly underwater.
With 8ft wide wings, and the ability to go to a depth of 1600ft, the Super Falcon can 'fly' underwater using a "downward lift" motion rather than sinking and rising like traditional submarines.
The craft is able to stay positively buoyant despite travelling at depth at a speed of four to five knots. If the engines are turned off it simply floats back up to the surface.
Hawkes says that unlike more conventional submarines the Super Falcon is incredibly quiet so it attracts sea life rather than scares it away.
"These are very wealthy individuals getting extraordinary machines that can go and do really cool things," said Hawkes.
The Super Falcon takes two people - although Hawkes says potential owners can order a three person model. Richard Branson has already bought one of Hawkes' creations for his own personal use, as well as taking on the DeepFlight Challenger, a submarine designed to travel to the deepest depths of the ocean. The underwater planes are also available to hire, but at a still titanic figure of $10k a day.
King Abdullah II of Jordan hired it for six weeks and invited local dignitaries, as well as schoolchildren, aboard.
Pilot training programmes cost $15,000 for three days and it's Hawkes himself who issues the certificates. He says the fact that underwater flying is such a new enterprise makes it much harder to regulate:"In the early years of aeroplanes nobody had licenses, nobody knew what the regulations were so we are right in that era of starting up something so new that nobody really knows what needs to be done.
"The rules and regulations are a little bit murky."
The DeepFlight underwater aeroplane (DAVID BUSH)
When Hawkes and Richard Branson took a dive in it last year they came face to face with a great white shark whose fin was just inches from the Super Falcon's wing.
Hawkes said: "There was some risk, we had discussed that. Nobody really knew what was going to happen."
"When you do things for the first time you really don't know what to expect."
"She certainly could have chewed off a wing but we didn't think she could really harm us."
The vehicle is equipped with emergency 'gas bags' to enable it to surface quickly and 24 hours of life support, although the batteries that operate it only have enough energy for eight hours.
Hawkes is hoping, eventually that the underwater plane will be seen at luxury resorts since it does not necessarily require a launch vehicle.
Rival Triton is manufacturing similar craft.
But none of these, says Hawkes, resemble aeroplanes and allow their pilots to play with animals.
"The Super Falcon is built for incredible new encounters, and we are having them. Most people have never been able to experience anything like it before."