Frode Weierud explains the purpose of this encryption system.
"These disks were used to prepare coded recognition signals. In
total there were five large and five small disks. The small
disks carried the code names: Schmidt, Schilling, Schneider,
Schulze and Seidel - all of these being German family
surnames. The large disks carried the code names: Eberhard,
Ernst, Erasmus, Egbert and Emil - all German first (given)
names. A small disk would be placed on top of a large disk, and
the correct combination given as a complete name e.g. Egbert
Schneider. Exactly how the disks were used to encode the
recognition signal is not known at this time. When the large and
small disks are mated, they always render the initials
"ES".
ES probably stands for Erkennungssignal (Recognition
Signal). The reference number M.Dv. Nr. 111 probably refers to
the disks themselves while the instructions for their use is
probably given in the document "Auszug aus der
"E.S.-Vorschrift" und Vorschrift "Der Erkennungsdienst" für
U-Boote, Berlin 1940, M.Dv. Nr. 75a. (Extract from
Recognition Signal Instructions and Instructions for the
Recognition Service for U-boats, Berlin 1940)."
