Holly Johnson visits Hamburg to explore how marathon sessions in smoky cellars, and friendships with local teenagers, helped create the incredible chemistry that turned a British beat group into the all-conquering Beatles.
The invasion of British bands into the red light district of Hamburg began in 1960 when German promoters realised that British rock 'n' rollers were cheaper to hire than American ones.
They were a five piece group when they arrived in the Reeperbahn in the back of manager Allan Williams' van in August 1960.
John, Paul and George were accompanied by Stuart Sutcliffe on bass and Pete Best on drums.
From August to October 1960, the Beatles were the house band at the Indra Club where they played four hour sessions every night for 30 marks each and slept in a tiny room above a local cinema.
From October to the end of the year, they were promoted to the nearby Kaiserkeller.
Not only were the Fab Five improving their sound during these marathon gigs, they were also developing friendships and the identity that would set them apart.
At the time, young people in Hamburg were typically members of one of two distinct tribes: the Rockers and the Exis (Existentialists).
They were 'enemies' occupying separate territories - the 'rock caves' and the jazz clubs.
When Exi Klaus Voorman was walking through the Grosse Freiheit on night in October 1960, he stopped outside the Kaiserkeller club to listen to the music.
Liking what he heard, he went inside to see Rory Storm & The Hurricanes (featuring Richard Starkey on drums) in full flight.
After the break, fellow Liverpudlians The Beatles took to the stage.
The day after first seeing The Beatles at the Kaiserkeller, Astrid arranged a photo session with them at the city fun-fair.
These stark candid images, which would be endlessly reprinted, established a distinct style for the group, as would Jurgen Vollmer's photos of the band.
A Vollmer picture of John standing in the doorway in the port district would later adorn the cover of Lennon's Rock 'n' Roll album, accompanied by the strap-line: 'You shoulda been there!'
It was an unlikely collision of young people from different cultures that would create a world-beating chemistry.
Where The Beatles had the sound, the Exis had the style.
Exis always wore black, with white collars or ruffs and their hair was pilzen kopf" - "mushroom head" in style.
"The Beatle haircut was in fact a Jurgen haircut" says Paul Mccartney.
Astrid began a relationship with Beatles bassist Stuart Sutcliffe and they were engaged by the time The Beatles returned to Liverpool in November.
They were back in Hamburg the following spring for 98 performances at the Top Ten Club.
And in June, they made their first professional recordings, with fellow British rocker Tony Sheridan.
The band recorded Ain't She Sweet, the instrumental Cry For A Shadow (a rare Harrison/ Lennon composition) and backed Sheridan on his version of My Bonnie.
Sheridan's single would reach the German Top 30 and would alert Brian Epstein to the existence of The Beatles when he was asked for a copy in his record shop in Liverpool.
Stuart Sutcliffe left the Beatles to stay in Hamburg with Astrid and pursue his career as a painter.
The Beatles returned to the city in April 1962 for a final residency at the Star Club only to learn of Sutcliffe's premature death when they met Astrid at Hamburg airport.
Love Me Do was just six months later.
The impact of Hamburg on The Beatles and the friendships they made there would endure.
Astrid continued to photograph the group after Sutcliffe's death while Klaus Voorman designed the sleeve for Revolver and later became a member of the Plastic Ono Band.
And as far as John Lennon was concerned, the band were never better than when in the thick of an all night session on the Reeperbahn.