Were the movie's underwater shots of the Titanic wreckage real?

RMS Titanic

Yes. Most of the underwater shots of the Titanic wreckage are real. In 1995, James Cameron hired the Russian vessel Akademik Mstislav Keldysh and its two submersibles.

He made a total of twelve dives to film the underwater close-ups at a depth of 12,500 feet below the North Atlantic. Special cameras and housings were designed to withstand the 6,000 pounds per square inch of water pressure

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Each dive lasted approximately fifteen hours, but the cameras could only store 500 feet of film, which meant that only twelve minutes of footage could be shot per dive. As a result, a few of the underwater shots had to be faked.