By 1963 the newspapers were calling it "Beatlemania" - and there was no doubt that Britain was in love with The Beatles.
Screaming fans clogged the streets around the London Palladium when the Liverpool rock group starred in a TV show, caused traffic jams at airports - incidentally delaying the new Prime Minister - and bought enough copies of She Loves You to keep it at number one for four weeks.
The "Fab Four" - or "Mop Tops", as the press dubbed its new heroes - reached their greatest pinnacle yet when they topped the bill at the Royal Variety Performance in London. It seemed even the Royals had succumbed to the charm of John, Paul, Ringo and George. Yeah, yeah, yeah.
But Beatlemania was not to remain a uniquely British phenomenon.
The Beatles flew into Kennedy Airport in New York in February 1964 and met their most ecstatic reception to date. Urged on by disc jockeys, who had been broadcasting constant updates on the progress of Pan-Am flight 101, thousands of American teenagers packed the airport to scream their adulation.
They broke through a police cordon, then formed a Beatles motorcade that followed their heroes all the way to the city's Plaza Hotel.
The following night they appeared live on The Ed Sullivan Show, once the springboard for Elvis, which put them into every American living room.