I suspect that it was an administrative appointment. He would have been responsible for the safe custody of and accounting for what we now call “crypto”; issuing it to users (probably the aircrew and the signals personnel), changing it on given dates and destroying it securely when it was out of date or In his case, when you are about to be overrun!
He may also have been responsible for encoding and decoding secret messages but not cracking the enemy’s codes.
One of the many unsung responsibilities that keep a force operating.