Director James Cameron was a Big Deal in 1986, following the success The Terminator and Aliens. If we also factor in his screenplay for Rambo: First Blood Part II, which was heavily rewritten by Sylvester Stallone but nevertheless retained his name on the credits, Cameron was a pivotal part of some of the biggest action movies of the 80s.

It makes sense, then, that rival studios would be keeping their ears open for whatever Cameron decided to do next; his career was on a clear upward trajectory, and there was little reason to assume that his next movie wouldn’t be an even bigger hit. Cameron began writing The Abyss – based on an undersea premise he’d come up with as a teenager – in 1986, finished the screenplay at the end of the following year, while filming got underway in the summer of 1988.

Filming on The Abyss was, famously, a nightmare. With his reputation at new heights, Cameron used his Hollywood clout to attempt something new in a Hollywood movie: rather than fake his underwater sequences, he shot a considerable percentage of them for real, in a colossal water tank located in South Carolina. As a result, The Abyss‘ shoot dragged on for months as Cameron and his cast and crew – among them Ed Harris, Mary Elizabeth Mastrantonio, and Michael Biehn – spent gruelling hours submerged in water.

The Abyss‘ huge expense and slow gestation meant that other, rival producers had at least a chance of beating 20th Century Fox’s potential blockbuster to the punch. Of the other undersea films, DeepStar Six may have come out in cinemas first, but Leviathan actually went into production much earlier. We know this thanks to an interview with DeepStar Six director Sean S. Cunningham (of Friday The 13th fame), who in a 1989 interview admitted that he was aware of Leviathan‘s existence before his own sea movie went into production.

“I was always aware of the fact that Leviathan was out there,” Cunningham told Starlog magazine, “and so I had to make a calculated decision last winter [1987-1988] as to whether or not I ought to beat them to the marketplace. I wanted to be first or I didn’t want to do it.”