The ominous tones of the now-famous “shark theme” (composed by John Williams and performed by tuba player Tommy Johnson) mark the arrival of Hollywood’s first major summer blockbuster on this day in 1975, when the director Steven Spielberg’s thriller Jaws debuts in U.S. theaters.

Based on the best-selling book by Peter Benchley, Jaws takes place in the fictional resort town of Amity Island, where police chief Martin Brody (played by Roy Scheider) learns that a young woman has been killed in a probable shark attack. Though greedy town officials want to cover up the threat to tourist business, another attack forces Brody to enlist the help of a marine biologist (Richard Dreyfuss) and a shark hunter (Robert Shaw) to try to catch the lethal beast, which turns out to be an enormous great white shark.

Producers Richard Zanuck and David Brown hired Spielberg for Jaws before the release of the then-27-year-old director’s first feature, 1974’s The Sugarland Express, which they also produced. The shooting, off the coast of Martha’s Vineyard, went much longer than scheduled, and the film’s budget ballooned from $4 million to $8 million. According to a 1982 article about Spielberg in TIME magazine, executives at Universal (which co-produced the film with Zanuck and Brown) even threatened to shut down production at one point and put “Bruce”–the mechanical shark used in the film–on display as part of its Universal City tour.

Instead, Universal opted to give Jaws a wide release instead of rolling it out to a small number of theaters first, as had been conventional practice up to that point. It opened nationwide on close to 500 screens (a small number compared to one of today’s big releases, which go out on 3,000-4,000 screens) but sizeable at the time. A $700,000 marketing campaign on network television preceded the film’s release, helping it to earn some $7 million in its opening weekend alone. Up until that time, summer had been seen as a period when producers would release films they considered weak, but Jaws ushered in the era of the summer blockbuster, as well as the studio practice of launching massive marketing campaigns to hype their films. Eventually shown in nearly 700 U.S. theaters, Jaws became the first summer mega-hit, racking up an impressive $260 million at the domestic box-office. All told, the film would gross some $450 million worldwide and establish Spielberg (who would strike more summer box-office gold with hits such as 1982’s E.T.: The Extra-Terrestrial) as the pre-eminent creator of summer movie magic.