Cameron enlisted engineers at Australia's Acheron Project Pty, specifically co-designer Ron Allum, who Cameron called the "only other parental supervision" on the project, and student engineers.
"We did this in secrecy because we didn't want to tell the world we were doing something we didn't know we could do until we were confident we could do it," Cameron says.
Allum says Deepsea Challenger had to be built to withstand more than 16,500 pounds per square inch of pressure, meaning several tons of force is exerted on each part of the sub. Allum says it's enough to "compress a block of steel."
"At that depth, everything compresses, even the sea water compresses," he says. That means that submerging can get difficult (think of trying to push a basketball to the bottom of a pool). To get it to the bottom, the team affixed a 1,100 pound weight, which has to be released on the way up.
"When we're descending, we're gaining buoyancy, but when we're ascending, we're losing it," he says. "That means if we got our calculations wrong, we might only come up three fourths of the way and we'd just be drifting in the currents indefinitely."
Allum says it's unlikely many more manned submarines designed to reach the deepest parts of the ocean will be built as robotic subs get more sophisticated, cheaper and come without the inherent risk that manned exploration brings. But robotic subs won't ever be able to replicate the feeling that comes with being miles beneath the ocean, he says.
"I've been down in this vehicle [on test missions to a depth of about a mile] and it's a tremendous experience. To go caving and experience it with your own eyes – to bring back a rock sample you've selected rather than doing it robotically – is absolutely amazing," he says. "I think in the future most of it will be robotic, but I still think we should have manned vessels."
Though Woods Hole doesn't have any immediate plans to put Deepsea Challenger back into the water, Gallo says Cameron's trip to the bottom of the Mariana Trench won't be its last mission. Cameron is coy about his plans, but Gallo says the director almost certainly will pilot it once again.
"We're looking at who will dive this next – my bet is it will be James Cameron himself," Gallo says. "I know he's working on Avatar 2, 3 and 4, but if he can stay away from Deepsea Challenger for a few years I'd be very surprised."