Millions of years ago, man in his evolution may have emerged from the sea to adapt himself to a land environment. With projected population curves spiraling upward, man may have to return to his primordial habitat to achieve the elbowroom necessary for survival on this planet. Captain Jacques-Yves Cousteau, the noted French undersea explorer and scientist, is convinced that colonization of the sea floor by the human species will be realized before the turn of the 21st century. Therefore, man must condition himself, through the experience of prolonged submergence, to readapt to the strange, hostile, and silent world of the briny deeps. What is it like? The eyewitness report of a world-famous news commentator vividly describes the weird, awesome, and mysterious sights he viewed at a depth of 650 fathoms when he traveled as an observer on a recent dive aboard the Deepstar-4000. But pragmatically, in terms of contemporary applications, the manned, deep-diving submersible is indispensable in the execution of a comprehensive ocean-bottom survey in which the positive identification and detailed analysis of unusual or significant topographical features must be made.