Between 17 and 20 July 1914, "Monarch" took part in a test mobilisation and fleet review as part of the British response to the July Crisis. Arriving in Portland on 25 July, she was ordered to proceed with the rest of the Home Fleet to Scapa Flow four days later to safeguard the fleet from a possible surprise attack by the Imperial German Navy. Following the outbreak of World War I in August, the Home Fleet was reorganised as the Grand Fleet, and placed under the command of Admiral Sir John Jellicoe. On 8 August, "Monarch" was conducting gunnery practice south-east of Fair Isle when she was unsuccessfully attacked by a submarine-fired torpedo. This was probably a false alarm as the area was too far to the west of the German U-boats' patrol zones to be likely. , however, has been suggested as a candidate for the attack, although the boat was sunk the following day with the loss of all hands and the truth will never be known.