Call it PDSD: Post Directing Stress Disorder. After completing work on his adaptation of Peter Benchley’s novel Jaws in 1974, Steven Spielberg nearly had a nervous breakdown. The mechanized shark rarely worked, shooting on the water was unpredictable, and the budget had swelled to $12 million—nearly four times what an average film of the time cost. It seemed reasonable to expect a disaster.

Instead, Jaws became the first film in history to gross $100 million and helped usher in the concept of the "summer blockbuster." Universal immediately wanted a sequel; Spielberg, owing to a wealth of opportunities and still reeling from the difficulty of shooting the original, declined.

Later, he would (very) briefly have a change of heart.

Jaws 2 began production in June 1977 to meet a summer 1978 release date. The studio hired John D. Hancock (1973's Bang the Drum Slowly) to direct, but Hancock spent only a month shooting before departing: He and the studio were reportedly at odds over the tone of the sequel. Before Universal secured television director Jeannot Szwarc to replace Hancock, they approached over 20 different names. None wanted to try and follow up the most successful film in history with a project that was already in trouble.

According to Joseph McBride’s Steven Spielberg: A Biography, beleaguered Universal executives Richard D. Zanuck and David Brown received a call from Spielberg while he was in post-production on Close Encounters of the Third Kind. The director had heard of the problems they were having and apparently felt some responsibility to both the franchise and the studio. Zanuck and Brown started to negotiate a deal for him to return to the series, and Spielberg spent the weekend of July 4, 1977 coming up with an idea.

Spielberg dismissed the script Universal was already working with—one that had another shark returning to Roy Scheider’s Amity beachfront vacation spot—and instead pitched a prequel about the real-life sinking of the USS Indianapolis in 1945 that saw dozens of sailors killed by feeding sharks. The incident had inspired actor Robert Shaw's speech in the original film:

While Spielberg and Universal had different opinions on why he wound up not doing it—Universal chief Sid Sheinberg said they couldn’t wait a year for Spielberg to be free from Close Encounters, while Spielberg maintained he ultimately decided a sequel would be “corporate business” that didn’t enthuse him—the Szwarc-directed film made its original release date and became the highest-grossing sequel of its time.

While it may never be tied to the Jaws franchise, the USS Indianapolis could still be headed for theaters. In 2015, Robert Downey, Jr. optioned a script that recounts the story. (And other big-screen retellings do exist.) Spielberg, of course, never returned to shark-infested waters: 1983's Jaws 3-D and 1987's Jaws: The Revenge were made without his involvement.