THE LAST FRONTIER

Sometime this fall, if all goes well, a revolutionary new undersea vessel will be lowered gently into the waters of Monterey Bay for its maiden voyage. Named Deep Flight I, the 14-ft.-long, 2,900-lb. vehicle is shaped like a chubby, winged torpedo but flies like an underwater bird. Compared with the hard-to-maneuver submersibles that now haul deep-sea explorers sluggishly around the oceans, Deep Flight is an aquatic F-16 fighter. It can perform barrel rolls, race a fast-moving pod of whales or leap vertically right out of the sea. With a touch on the controls, a skilled pilot--who lies prone in a body harness, his or her head protruding into the craft's hemispherical glass nose--can skim just below the ocean's surface or plunge thousands of feet below.

More than 35 years after the bathyscaphe Trieste took two men, for the first and last time, 35,800 ft. down to the deepest spot in the world--the Mariana Trench's Challenger Deep just off Guam in the western Pacific--undersea adventurers are preparing to go back. Last March a Japanese robot scouted a tiny section of the bottom of the 1,584-mile-long crevasse and sent back the first real-time video images of deepest-sea life. And in laboratories around the world, engineers are hard at work on an armada of sophisticated craft designed to explore--and in some cases exploit--the one great unconquered place on earth: the bottom of the sea.

The irony of 20th century scientists venturing out to explore waters that have been navigated for thousands of years is not lost on oceanographers. More than 100 expeditions have reached Everest, the 29,028-ft. pinnacle of the Himalayas; manned voyages to space have become commonplace; and robot probes have ventured to the outer reaches of the solar system. But only now are the deepest parts of the ocean coming within reach. "I think there's a perception that we have already explored the sea," says marine biologist Sylvia Earle, a former chief scientist at the National Oceanographic and Atmospheric Administration and a co-founder of Deep Ocean Engineering, the San Leandro, California, company where construction of Deep Flight I began: "The reality is we know more about Mars than we know about the oceans."

That goes not only for the sea's uttermost depths but also for the still mysterious middle waters three or four miles down, and even for the "shallows" a few hundred feet deep. For while the push to reach the very bottom of the sea has fired the imagination of some of the world's most daring explorers, it is just the most visible part of a broad international effort to probe the oceans' depths. It's a high-sea adventure fraught with danger, and--because of the expense--with controversy as well.

But the rewards could be enormous: oil and mineral wealth to rival Alaska's North Slope and California's Gold Rush; scientific discoveries that could change our view of how the planet--and the life-forms on it--evolved; natural substances that could yield new medicines and whole new classes of industrial chemicals. Beyond those practical benefits there is the intangible but real satisfaction that comes from exploring earth's last great frontier.