From Titanic movie wiki--copied and pasted.

The story could not have been written better had it been fiction ...The juxtaposition of rich and poor, the gender roles played out unto death (women first), the stoicism and nobility of a bygone age, the magnificence of the great ship matched in scale only by the folly of the men who drove her hell-bent through the darkness. And above all the lesson: that life is uncertain, the future unknowable ... the unthinkable possible. —James Cameron[53][54]

James Cameron has long had a fascination with shipwrecks, and for him Titanic was "the Mount Everest of shipwrecks".[55][56][57] He was almost past the point in his life when he felt he could consider an undersea expedition, but said he still had "a mental restlessness" to live the life he had turned away from when he switched from the sciences to the arts in college. When an IMAX film, Titanica, was made from footage shot of the Titanic wreck, Cameron decided to seek Hollywood funding for his own expedition. It was "not because I particularly wanted to make the movie," Cameron said. "I wanted to dive to the shipwreck."[55]

Cameron wrote a scriptment for a Titanic film,[58] met with 20th Century Fox executives including Peter Chernin, and pitched it as "Romeo and Juliet on the Titanic".[56][57] Cameron said the executives were unconvinced of the commercial potential, and had instead hoped for action scenes similar to his previous films.[13] They approved the project as they hoped for a long-term relationship with Cameron.[13][14][24]

Cameron convinced 20th Century Fox to promote the film based on the publicity afforded by shooting the Titanic wreck,[58] and organized several dives over a period of two years.[53] He also convinced 20th Century Fox that shooting the real wreck for the film scenes, instead of simulating it with special effects, would provide value: "We can either do [the shots] with elaborate models and motion control shots and CG and all that, which will cost X amount of money – or we can spend X plus 30 per cent and actually go shoot it at the real wreck."[56]

The crew shot at the wreck in the Atlantic Ocean 12 times in 1995. The work was risky, as the water pressure could kill the crew if there were a tiny flaw in the submersible structure.[14]