I saw the film quite recently on UK TV (possibly SKY satellite TV).
The title is correct.  The allied operators were emptying the diamond
exchange with the collaboration of the diamond owners. The organ was
played to signal the appearance of the Germans on the scene. The organ,
or a mock-up of it, was used for protection from flying bullets with the
bandmaster and clochettes coming in for some horrible attacks!

Unfortunately, when the organ grinder, English actor Melvyn Hayes, was
hit (he carried on playing while all this mayhem was going on!) the organ
"wound down" as per a vinyl record, not as per an organ running out of
power, the frequency falling as the grinder did!   Ah well.

Phil Benson