The cruiser was detached from Scapa Flow after Russian forces captured German code material in the Baltic. Theseus sailed to Alexandrovsk and returned with two Russian couriers and the documents. The material was formally handed to First Lord Winston Churchill and then passed to Room 40. Her delivery connected an operational naval voyage with the intelligence breakthrough that allowed Britain to exploit German communications.
Chapter · 55:44-56:29
HMS Theseus brings German codebooks to Room 40
Theseus carried captured German code material and Russian couriers from Alexandrovsk to Britain for transfer to Churchill and Room 40.