Doesn't look German to me. If it is British military then I believe it will be post WW2 when they switched to the [2 numbers] [2 letters] [2 numbers] format. The letter codes AA to AZ were RAF, RN is Royal Navy and everything else was Army.
Doesn't appear to be a British plate format either.
Have a browse through this site, hopefully there'll be a match somewhere:
License Plates of Europe