The Royal Navy's Room 40 had intercepted and decrypted German radio traffic containing plans for a German attack on Scarborough, Hartlepool and Whitby in mid-December using the four battlecruisers of "Konteradmiral" (Rear-Admiral) Franz von Hipper's I Scouting Group. The radio messages did not mention that the High Seas Fleet with fourteen dreadnoughts and eight pre-dreadnoughts would reinforce Hipper. The ships of both sides departed their bases on 15 December, with the British intending to ambush the German ships on their return voyage. They mustered the six dreadnoughts of Vice-Admiral Sir George Warrender's 2nd BS, including "Monarch" and her sister ships, "Orion" and "Conqueror", and Beatty's four battlecruisers.