June 20 marks the 40th anniversary of “Jaws,” which revolutionized the industry — even though the numbers seem pretty quaint by today’s standards.

In its first three days in 1975, the film earned $7 million, jumping to $14 million in its first week. In its 59th day of release, the Universal movie passed the $100 million mark. That’s chump change in the current world, but in those days, “Jaws” was jaw-dropping.

The Steven Spielberg film is credited with inventing the wide release, which is not true. It is also credited with inventing the summer blockbuster. That’s partially true, but it was really the one-two punch of “Jaws” and “Star Wars” two years later that set the template for Hollywood’s summer obsession.

At the time, there was no set pattern for opening a big film. The 1939 “Gone With the Wind” had opened in December; “The Sound of Music” and “The Godfather” each debuted in March (in 1965 and 1972, respectively). So some thought the summer phenomenon of “Jaws” was a fluke. It was clearly a “summer movie,” with its seaside setting, based on the 1974 Peter Benchley bestseller, a popular “beach read.”

But the “Jaws”-“Star Wars” combo — the latter opened in late May — confirmed that summer was the perfect time for a blockbuster. It also confirmed that TV was a key factor in marketing.

On April 9, 1975, two months before “Jaws” opened, Variety ran a Universal ad bragging the film would be “Backed by the biggest national prime-time T.V. spot campaign in motion picture history!” It listed 23 TV shows that would air 30-second spots for the film, with the ads running June 17-20 on such series as “Happy Days,” “The Waltons,” “Sanford and Son” and “Rockford Files.”

“Jaws” opened at 409 U.S. theaters (Variety and the studios counted theaters, not screens). The opening was only a slight jump from the 1972 “The Godfather” (365 venues), but both were a big drop from “Beast From 20,000 Fathoms” more than two decades earlier. In June 16, 1953, Daily Variety reported Warner Bros. would use heavy TV and radio ads as the film opened at a record 1,422 bookings. “Beast” was a hit. So clearly, Hollywood was a little slow on the uptake.

Other genre films had opened wide, but the philosophy was usually grab the money and run, before word of mouth spreads. The distinction of “Jaws” was not the size of the debut, but its persistence. By Day 17, it had expanded to 464 theaters; it hit a whopping 954 screens by day 59, when it reached the $100 million milestone.

The success was a big relief for Universal, Spielberg, and producers David Brown and Richard Zanuck. The film had been scheduled for 55 days of shooting, which extended to 159 days, thanks to malfunctioning mechanical sharks and the difficulty of filming in the ocean. And the budget doubled, to $7 million.

But the film was such a hit, it earned its costs back in three weeks. And helped create film history.