General Heinrich Mueller, played by Martin Kosleck, was not a fictional character - he was the real head of the Gestapo and held the rank of major general in both the SS and the state police agency.
In this episode, Carter is pressed into service to 'pick the pocket' of Captain Geissler. Normally Newkirk would have done it, but he was busy watching the phone line in case Major Strauss made another call to General Mueller.
This is the only episode where a recording is made on an actual record using their own recording equipment. Normally they would have used a wire recorder to record General Mueller's voice. Note: They also made a record in The Big Record (1970), but they used a recorder provided by Klink.
General Mueller's staff car has license plate number is DXR 499.
Klink's staff car license plate is WH 54693.