To break the coded arrangement of the alphanumeric serial designation, Langer worked with banking experts, examining records of currency from the previous 20 years in order to replicate the correct order.[5] No records were kept by Operation Andreas and the method of how the Germans identified the correct sequences is not known; the paper historian Peter Bower states that it is possible that techniques adapted from those used in cryptanalysis were used to break the sequences.[28] The German engravers working on the engraving plates struggled to reproduce the vignette of Britannia, which they nicknamed "Bloody Britannia" because it was so difficult.