A look back at the decades of effort that culminated in the deep sub Alvin reaching the ocean floor, and a look forward to what's next now that Alvin's retiring. In the summer of 1964, the first tentative dives into the shallow waters of Cape Cod, Massachusetts, were made by the new deep diving submarine, Alvin. The sub, built for the US Navy and operated by the Woods Hole Oceanographic Institution (WHOI), was to become arguably the most successful research submarine ever. We go on a typical Alvin science dive, accompanying a biologist as the WHOI pilot takes the sub down 8,000 feet into the pitch darkness of the Galapagos Rift, to collect samples. It was here in 1977 that people first saw, from the Alvin, a kind of life that we had never known existed on the planet - colonies of giant clams, tube worms, fish and crabs living not on sunlight but on bacteria that consume the gases dissolved in water gushing from warm, undersea volcanic water vents. Back at WHOI on Cape Cod, Alvin's successor is now taking shape - in computer models, and wood and fiberglass mockups. The new sub will retain the same time-tested basic components as Alvin - the massive spherical forged titanium pressure hull, the tough, pressure-resistant glass foam flotation material. But working conditions for scientists will be greatly improved - more room, faster dive and ascent speeds, access to almost the entire global ocean floor, and the ability to actually see the same outside view as the pilot.