(CNN) -- In early 1964, the British Invasion dominated American airwaves.
From WABC in New York to KRLA in Los Angeles, California, the radio dial pulsed with the Beatles and their brethren, injecting more excitement into a medium that was already jumping with crazy DJs, cash-call contests and battles of the bands.
But the British Invasion on British radio? Good luck.
While Beatlemania took over the world, Great Britain's ever-so-proper BBC filled its air with a melange of news, gardening tips, dramas, plummy announcements and maybe -- maybe -- the occasional pop record. At night, the radio dial was almost empty, as many stations signed off at nightfall.
Enter the pirates, entrepreneurs and radio personalities who set up shop on ships just outside British territorial waters and broadcast a powerful signal back into the motherland. The era is the subject of the new film "Pirate Radio," starring Philip Seymour Hoffman, which opens Friday.
The peak of the so-called "pirate radio" stations was only three years -- from 1964 until 1967 -- but in that time the freewheeling broadcasts, many staffed by Americans, brought a party atmosphere and a pop music variety to a country that had never experienced such a sound.
"Everything was very conservative, controlled by the old guard [there]," recalls Bruce "Cousin Brucie" Morrow, a leading American DJ on the No. 1 station in the country, New York's WABC. The British DJs, Morrow recalls, would come over and study Morrow and his counterparts, staying for weeks at a time. "The only way they could get rock 'n' roll was by recordings or somebody would smuggle something in from the United States. ... And young people wanted their own music."
Radio Caroline, the first of the notable pirate radio stations, went on the air on Easter weekend 1964. Though it would be considered relatively staid by modern ears, it was a sensation in Europe. Among its early competition was Radio Atlanta, founded by American Top 40 pioneer Gordon McLendon, whose idea for a pirate station had actually been pirated itself by Caroline founder Ronan O'Rahilly. (Another station, the non-pirate but expansive Radio Luxembourg, had been focusing on the teen market for several years but was far more restrictive in its programming.)
The pirate stations were thrilling to British youth.
"You could jam that transistor way up tight against your ear and you'd hear nothing but righteous music all day long," wrote pop critic Nik Cohn in his history of rock music, "A Wop Bop a Loo Bop a Lop Bam Boom." "Nothing unpop, no crap broke in on you."
The stations were also proudly commercial, unusual in the public broadcasting world of Europe. With a growing teen market, a number of investors saw dollar signs on the pirate boats.
Among them was Don Pierson, a businessman from Eastland, Texas. Pierson, whom his son Grey describes as "beyond colorful," had been a car dealer, banker, Eastland mayor and local character when he saw an article on Radio Caroline in a newspaper.
As an unreleased documentary about Pierson, "Swinging Radio England," details, he immediately seized on the idea for his own pirate station.
"He was born without the gene that tells you what you can't do," says Grey Pierson, now a Dallas-area attorney.
Don Pierson, who would make a dandy subject for a movie himself, was an admirer of McLendon's Dallas station, KLIF, one of the most manic in the country, and based his Wonderful Radio London on KLIF's format. After losing control of that station months after it went on the air in December 1964, he started another pirate broadcaster, Swinging Radio England.
The pirate stations lived up to their swashbuckling moniker. The staffs would share quarters on the old, barely refurbished boats for weeks at a time, creating a hothouse atmosphere separate from the broadcasts themselves. Guests would have to be ferried in and out.
Roger Day, one of the Radio England DJs, describes it in the documentary as "a Boy Scout camp gone mad."
Eventually, camp came to an end. Radio England, which was beset by technical difficulties, shut down in late 1966. More important, the British government, which frowned on the pirates, made their lives difficult by haranguing the broadcasters.
"In 1967, the government passed the Marine Broadcast Offences Act [which effectively outlawed pirate stations]," recalls Morrow, an encyclopedia of radio knowledge and the author of the new "Rock and Roll: And the Beat Goes On." "That's how serious pirate radio got."
The act became law in August 1967. Six weeks later, the BBC launched Radio 1, its capitulation to the youth culture. The first DJ on the air was a pirate veteran, Tony Blackburn; it used the PAMS jingles beloved by American stations, and the first record it broadcast was "Flowers in the Rain" by the rebellious UK band the Move.
There are few reminders of the pirate radio era today. The Who paid tribute to Radio London on its 1967 album, "The Who Sell Out," and some of the personalities, including Blackburn and the late Kenny Everett, established long careers.
But mostly pirate radio established that, in Britain, rock 'n' roll was here to stay.
Morrow, who was invited to guest DJ on Caroline but declined for various reasons (not the least of which, he said, is "I don't like boats"), says he was entranced by the spirit of the buccaneers.
"They loved the American radio style," he says. And the audience responded in kind: "When a tidal wave starts, you can't stop it."