Yes, Cameron has done plenty of underwater docos before. He's been down to his beloved Titanic (a mere 3800m) many times and the Bismark (5700m) in Russian-made Mir submersibles.
And his passion for the deep has manifested itself in his movies - most obviously in The Abyss and Titanic, and, less obviously, in the immersive underwater-inspired look of Avatar's world of Pandora, a planet where humans require breathing apparatus.
The National Geographic-backed JCDSC follows Cameron on a mission to repeat the feat of US Navy submersible the Trieste, which went to the deepest point of the Mariana Trench - the "Challenger Deep" - with two crew on board in 1960. No one has been that deep since.
That meant building something that would withstand the 16000psi, and bring back Cameron and his footage in one piece.
Cameron has been a scuba diver since he was 16. He started doing deep submersible diving in the mid 90s. Going to 11,000m was just the next stage. "I never saw it as a stunt. I saw it as a natural progression of work that had been done before."
Director James Cameron. Photo / Mark Thiessen, National Geographic
Still, this doco differs from Cameron's previous ones. Though the others also followed his adventures, this is as much about Cameron himself. He's shown balancing the duties of project manager and backer and guy who would die a spectacularly expensive death if it all went wrong.
Shots of him in meetings at the Sydney engineering firm where his Deepsea Challenger submersible was built show him as a flinty, hard taskmaster as he demands deadlines be met on a project where the research and development stage and actual engineering were never far apart.
Was he comfortable seeing so much of himself on screen?
"You know, I'm over it ... this was the first time I was really front and centre. I have always tried to endeavour, in the past films, to have other people really carrying the torch so I had to really recuse myself creatively as much as possible.
"I kept my focus on the expedition itself - getting the sub operational, learning how to pilot it effectively and bringing back the science."
Cameron didn't just sit on the bottom of the Mariana Trench for three hours then leave. He took seawater samples and - before the hydraulics and the starboard thrusters gave out - scooped up soil from the sea floor.
But is this his job or just a very expensive hobby underwritten by his well-paid other career?
"It depends when you ask the question. When I am on an expedition, the exploration and the science are the most important thing and the Hollywood film-making just sort of feeds that and funds it. If I am am working on a narrative film, like I am right now, that art form takes precedence.
Director James Cameron. Photo / Mark Thiessen, National Geographic
"Other people can do the science but not that many people can make the kind of films I make, so I should be doing that."
Cameron says while he's a better filmmaker than a marine engineer, the two pursuits have common skill sets.
"The difference is you have a different level of respect for the goalposts that you can't move when you are doing an expedition. Because you can't just do another take. You can't gloss over it with visual effects. You have to make things really happen in the real world with no smoke and mirrors.
"So I think there is a part of me that is very disciplined that that appeals to."
Certainly, the footage of Cameron heading to the bottom doesn't give away any signs of fear.
"Maybe it's the duck principal - you stay calm above the water and you are paddling like hell underneath. But no, I tend to be very analytical when I am actually doing the dive. I think the apprehension comes beforehand when you are running all the scenarios of what could go wrong.
"If something occurs to me in one of my paranoid fantasies, that is something we can do something about - I will get everybody together for a safety meeting. There are variables regardless of how well-engineered the vehicle is. If I had hit a fishing net, for example ... or I could implode.
Director James Cameron. Photo / Brook Rushton, National Geographic
"But I figured if I imploded I wouldn't feel anything. By the time my pain impulses reached my brain, my brain wouldn't be there. You kind of don't have to worry about it."
Cameron's wife, Suzy Amis, is seen in the doco doing quite a bit of worrying, while footage of their kids remind how much he's got at stake. "Suzy was out there on the expedition with us and I know she was very proud of being part of the expedition team, so I had no qualms about putting her in the film. Having the kids in the film really goes against the policy I have - except that I thought that it spoke so well to really what the film was about, which was inspiring kids and inspiring that sense of exploration and curiosity, that ultimately I agreed to let it in."
He's not sure if his younger kids realise that their dad's two jobs - director of the biggest movies of all time and underwater adventurer - aren't what most dads do, yet.
"It's all relative, right? If you've just grown up with all this crazy stuff, with films and expeditions around you, it doesn't seem strange to them. We try to keep the home life as conventional as possible."
That includes heading out this week from their Californian home for a spot of trick-or-treating. No, he's not painting the kids blue or turning one of them into a T-800.
Director James Cameron. Photo / Brook Rushton, National Geographic
"We have a vampire, a zombie and, I think, a wolf. I'm still racking my brain as to what I should wear to fit in with that motley crew. My personal assistant has to go out and buy some costume or I try to cobble something up. Gluing in vampire teeth or whatever it is. We take our Halloween very seriously - everybody gets involved."
Well, it sure would be bit of a long way to go door-to-door from his home-away-from-home in the Wairarapa to his neighbours' place.
"I think if we were going to do Halloween in New Zealand we'd do it in Wellington. We'll go knock on Peter Jackson's door in Seatoun and see how generous they are."
So how are those Avatar sequels going?
A scene from the movie Avatar.
When Timeout calls, James Cameron says he's in the middle of writing a scene for one of the three Avatar films.
"It's actually an action scene, which I love to orchestrate to the n-th degree on the page so I can change it all later," he laughs.
The sequels to the 2009 all-time box office champ are due to start production in Wellington early next year, with Cameron and family returning to New Zealand just after Christmas.
The first film is due out at the end of 2016.
"It's an enormous project, so people have to manage their expectations about how quickly we are going to bring these things to the screen.
"You know, the first Avatar movie was one of the biggest movies ever made in terms of its cost and logistics and so on, and 2, 3 and 4 are not going to be any different.
"Right now we are deep in the design process. We have the new characters, the new creatures, the new environments, all through the preliminary design phase. We've got rooms and rooms filled with fantastic art, so it's very exciting to see the world come to life. The next stage will be to start building them out in CG - standing that world up so we can navigate in it.
"We have had to upgrade our process quite a bit so we've been working with Weta Digital for the last couple of years to really make the pipeline more robust and more streamlined, because we really have to get more through it in a shorter period of time."
Who: James Cameron, director of well-known movies and man in deep water
What: James Cameron's Deep Sea Challenge 3D
When: At cinemas from November 6
James Cameron is featured on the cover of this week's TimeOut:
- TimeOut
