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Story highlights

"Jaws" opened on June 20, 1975, and broke box-office records

The film launched director Steven Spielberg's career

Explore your favorite films from each decade: Watch CNN’s “The Movies” Sundays at 9 p.m. ET/PT.

(CNN) —  

It should have been a waterlogged disaster.

The shoot ran too long and over budget, the script was still being written as scenes were filmed, the young director woke up every day fearing he would get fired, and the mechanical shark built for the movie sank to the bottom of the ocean.

And yet, 40 years ago this summer, people lined up around the block and around the world to get scared silly by “Jaws,” widely seen as the first summer blockbuster.

A horror story wrapped in an adventure, the movie tapped into our deepest fears about what dangers lurk beneath the ocean’s surface. Some people told screenwriter Carl Gottlieb that the movie, about a giant shark terrorizing a summer resort town, even made them afraid to venture into swimming pools.

Yes, the fake shark looks a little cheesy now. But in 1975, long before computers could create any spectacle onscreen, it was plenty terrifying.

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The movie overcame a troubled shoot to launch Steven Spielberg’s career as a master craftsman of popular entertainments. With its wide release and aggressive ad campaign, it also pioneered the current Hollywood model for how big-budget movies are springboarded into the market.

And it sparked a cultural fascination with sharks – especially great whites – that endures today in everything from IMAX documentaries to the “Sharknado” movies to the Discovery Channel’s annual Shark Week.

The original “Jaws” returned to select theaters nationwide on June 21 and 24, giving today’s moviegoers a rare chance to see it on the big screen. Which means that 40 years later, it’s still not safe to go back in the water.

Here’s a roundup of 21 salient and strange facts about the movie.

1. Spielberg, whose first film, “Duel,” was about a highway motorist being menaced by a mysterious tanker truck, was afraid of being typecast if he took the “Jaws” job. “Who wants to be known as a shark-and-truck director?” he complained.

2. None of the three main actors – Roy Scheider, Robert Shaw and Richard Dreyfuss – was the producers’ first choice for the parts. Robert Duvall and Charlton Heston were among those considered for Chief Brody, while Lee Marvin and Sterling Hayden were initially sought for Captain Quint, and Jeff Bridges was discussed for Matt Hooper, the marine biologist.

3. The movie’s script eliminated several subplots from Peter Benchley’s novel that Spielberg considered distracting, including an affair between Chief Brody’s wife, Ellen, and Hooper (Dreyfuss).

4. Location scouts considered filming locales across the United States but chose Martha’s Vineyard because they needed a summer beach resort town with a sheltered bay, manageable tides and shallow waters to make filming easier.

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5. Although the movie is set in midsummer, producers began filming in early May 1974 to avoid an actors’ strike that was scheduled to begi