Between 17 and 20 July 1914 "Neptune" took part in a test mobilisation and fleet review as part of the British response to the July Crisis. Arriving in Portland on 27 July, she was ordered to proceed with the rest of the Home Fleet to Scapa Flow two days later to safeguard the fleet from a possible German surprise attack. In August 1914, following the outbreak of the First World War, the Home Fleet was reorganised as the Grand Fleet, and placed under the command of Admiral Jellicoe. Most of it was briefly based (22 October to 3 November) at Lough Swilly, Ireland, while the defences at Scapa were strengthened. On the evening of 22 November 1914, the Grand Fleet conducted a fruitless sweep in the southern half of the North Sea; "Neptune" stood with the main body in support of Vice-Admiral David Beatty's 1st Battlecruiser Squadron. The fleet was back in port in Scapa Flow by 27 November and the ship began a refit on 11 December.