“All right, there’s a shark in the water,” a man bellows through a megaphone, a hint of melancholy in his voice. “He’s been killing people, legs have been bitten off, and there’s blood all over the place…”

It’s June 1974, and the water’s freezing. Dozens of extras, clad in trunks and bathing costumes, are bobbing about just off the beach of Martha’s Vineyard, Massachusetts, trying not to shiver. It may be summer, but the locals know that the water doesn’t warm up until late in the season.

The man holding the megaphone is a member of the production team putting together Jaws. For the then 26-year-old Steven Spielberg, Jaws is a decisive moment in his career. With the movie already starting to run over its originally planned $3.5 million budget, he knows that, if the movie sinks, so does his future as a filmmaker.

What Spielberg couldn’t have known, as he stood on that New England beach with his goose-pimpled extras, was that Jaws would become one of the most lucrative and important films in Hollywood’s history. It would also prove to be the most gruelling shoot of Spielberg’s career.