Graham Hawkes calls his products functional luxurious. As he explains it, they are “the same as a Ferrari but not a Rolls-Royce”—in other words, built for speed and not comfort.

But the two-seaters Hawkes makes are for cruising sea depths, not scenic routes. His San-Francisco-based company, Deep Flight Submersibles, started in the 1970s by building tiny submarines that allowed researchers to inspect the ocean floor. In the past three years, however, a demand for private minisubs has surfaced, as more people have been buying mega-yachts and stocking them with mega-toys like seaplanes, Jet Skis, kayaks, and speedboats.

No one knows just how many personal submarines are out there—the Coast Guard, incidentally, simply considers them boats—but anecdotal evidence suggests they have become more popular with nautical nabobs. And why not? If you feel like you’ve seen the world’s most comely coastlines and ravishing reefs, you can use a minisub to explore shipwrecks and spend time on the bottom of the sea.

“You’ve got unlimited access to the depths of the ocean,” says Mark Ragan, who gives lessons in his yellow (a popular color) two-person, 14-foot-long K-250 sub in Annapolis, Maryland. “You have the ability to dive whenever you feel like it without getting wet. At anchor in your yacht in the Caribbean, you just get in and go night diving.”

Today’s submarines can go faster and deeper than their predecessors, and they are easier to control than the Lotus Esprit S1 submarine car that James Bond steered in The Spy Who Loved Me. They can be as simple as a $18,000 homebuilt sub, or as elaborate as the immense underwater yachts that go for tens of millions of dollars.

Each sub, like the Wright brothers’ flying machines, is a one-off creation. One example is the $1.5 million, two-person Super Falcon, which Deep Flight started building in July for venture capital guru Tom Perkins. (Its name is derived from Perkins’ yacht, Maltese Falcon, which the sub will accompany.) By the time it’s delivered in May, the Super Falcon will have a modern fighter jet’s controls and be just as maneuverable. Its state-of-the-art electronics will project an artificial horizon along with speed, depth, and navigational information onto the canopy. “It’s all very familiar to anybody who flies an airplane,” Hawkes says.

Of course, that’s the Ferrari. The Rolls-Royce of personal subs is something like U.S. Submarines’ Phoenix 1000. The Phoenix is 213 feet long—compared with 252 feet for an early German U-boat—and can cruise at 16 knots underwater. (The vintage U-boat could do only 7.) It can cross the Atlantic submerged (so you can avoid the weather and still enjoy the view), and it’s infinitely more luxurious than a warship, with 5,000 square feet of living space, five staterooms, ports that offer a broad view, and common areas packed to the gills with leather and wood furnishings, all custom designed to the owner’s specifications. This submarine can even be equipped with its own sub, a two- to eight-person mini capable of diving up to 2,000 feet—or even functioning as an escape vehicle. The Phoenix price: $78 million.

A Phoenix-size submarine is best berthed at a pier, but most minisubs are made to be launched from a yacht. In a pinch, they can even be brought to the nearest body of water on a trailer. And surprisingly, one doesn’t need to be certified to operate one, since the Coast Guard regards them as small boats, whether above or below water. Homeland security concerns do apply, however. In August 2007, the New York City police department arrested artist Philip Riley for drifting within 200 feet of the Queen Mary II in his replica of the first personal submarine, the Revolutionary War-era Turtle. New York Police Commissioner Ray Kelly downplayed the incident as “marine mischief.”

Fortunately, miniature submarine technology has progressed a great deal since the original one-person, human-propelled Turtle was built more than 230 years ago. World War II-era U-boats could dive to 750 feet, but at lower depths, the extreme pressure forced rivets to pop out of the hull. Modern personal submarines can reach that depth with ease. Chronic adventurer Steve Fossett had Hawkes start building him the Deep Flight Challenger, a 14-foot-long sub capable of cruising the bottom of the 36,000-foot-deep Mariana Trench for up to four hours. Hawkes was ready to begin initial water tests on the vessel in September when Fossett disappeared while flying somewhere over Nevada.

But regardless of whether the sub they’re piloting is barely floating on the surface, like Philip Riley’ eggish Turtle, or can reach the depths that Steve Fossett hoped to see, owners always like to take their boats down a little further. “What you want to look at,” says Ellis Adams of Seattle, who owns a two-seat (“we could put three in there if you’re really chummy”) diesel electric known as the S-101, “is always 100 feet deeper than your maximum depth rating.”

These days, it’s not difficult to find personal vessels. At September’s Monaco Yacht Fair, for instance, Dutch company U-Boat Worx displayed its new two-place electric. The tiny $246,000 submarine is nice enough for the yacht and can dive up to 160 feet below the sea. U.S. Submarine has its economical two-person Triton 1000 listed in this year’s Neiman Marcus holiday catalog. The $1.44 million price is such a bargain that Neiman Marcus has already sold out its entire stock. Okay, so the store had only one, but U.S. Submarines is building another just for the catalog.

Check the internet for good buys too. That’s where Ellis Adams is advertising his S-101. Selling point: It is painted like an Orca whale. Bidding starts at $640,000.