On 26 August 1914, the German light cruiser had run aground in the Gulf of Finland; the wreck was captured by the Russian navy, which found codebooks used by the German navy, along with navigational charts for the North Sea. These documents were then passed on to the Royal Navy. Room 40 began decrypting German signals, and on 14 December, intercepted messages relating to the plan to bombard Scarborough. However, the exact details of the plan were unknown, and it was assumed that the High Seas Fleet would remain safely in port, as in the previous bombardment. Vice Admiral Beatty's four battlecruisers, supported by the 3rd Cruiser Squadron and the 1st Light Cruiser Squadron, along with the 2nd Battle Squadron's six dreadnoughts, were to ambush Hipper's battlecruisers.