The New York Times has a well-written article about the new Alvin replacement. There is also a 15 minute Science Times podcast and several photos of the 7 foot wide, 3 inch thick titanium sphere being molded (must see) as well as the above graphic proposing a hybrid option to use the new sphere inside the old Alvin body during the interim period. Here is an excerpt:
" The United States used to have several submersibles -- tiny submarines that dive extraordinarily deep. Alvin is the only one left, and after more than four decades of probing the sea's depths it is to be retired. Its replacement, costing some $50 million, is to go deeper, move faster, stay down longer, cut the dark better, carry more scientific gear and maybe -- just maybe -- open a new era of exploration.
Its architects at the Woods Hole Oceanographic Institution on Cape Cod describe it as "the most capable deep-sea research vehicle in the world."
Alvin can transport a pilot and two scientists down 2.8 miles, providing access to 62 percent of the dark seabed. The new vehicle is expected to descend more than four miles, opening 99 percent of the ocean floor to inquiry. But the greater depth means that the vehicle's personnel sphere and its many other systems will face added tons of crushing pressure.
. . .
Dr. [Cindy] Van Dover said one of the big payoffs would be the submersible's ability to dive deep.
"Depth is a big deal," she said. "It's hard to wax lyrical on the subject because we don't know what's there. So we can't guarantee a discovery. Yet we know that every time we extend our ability to go somewhere, we discover new things about how the planet works, about how life on the planet is adapted.""(emphasis mine)