A glamorous blonde.
The phrase was first used to describe Jean Harlow. Her US film 'Bombshell' was released in 1933. The blurb that went along with adverts like this one was:
"Lovely, luscious, exotic Jean Harlow as the Blonde Bombshell of filmdom."
By the time that the film was released in the UK the phrase had taken off and it was titled 'Blonde Bombshell' there.
See other phrases that were coined in the USA.