The scene in the harbour on such occasions was a busy one. Small craft of every nature were patrolling at the sight of a periscope; all guns were manned; torpedo nets, where fitted, were placed in position; and every effort was made to ensure that the Fleet was as adequately guarded by the available patrol craft as circumstances admitted. All large ships except the repair ships _Cyclops_ and _Assistance_ left harbour during the night, the _Iron Duke_ joining the 1st and 4th Battle Squadrons west of the Orkneys. At noon on the 17th Sir Stanley Colville, who had been requested to organise a careful search for the reported submarine, signalled that a submarine was believed to be inside Scapa Flow and had been hunted, but not actually located. Reports had been received that officers and men on board several of the destroyers, and the gunboat _Leda_, had seen the periscope of the submarine, and that a torpedo had actually been fired at one of the hunting vessels. It was, however, ascertained subsequently that this torpedo was one which had been accidentally discharged by one of our own destroyers. The accuracy or otherwise of these reports has never yet been determined with certainty, but many of the officers engaged in the search were convinced at the time that a submarine was actually inside, and that they had seen her. Indeed, a good many rounds were fired during the day at objects which were thought at the time to be a periscope. The reports signalled to me convinced me that, until the matter was cleared up with certainty, and until some more absolute security against submarine attack on the Fleet at anchor could be provided, it was courting disaster to base battleships or battle cruisers at Scapa Flow. We had seen in the loss of the _Hawke_ that enemy submarines could quite well operate in northern waters, and it was thought to be only a matter of time before they would attempt an attack on the Fleet in Scapa Flow, if indeed the attempt had not already been made. I decided, therefore, that it was necessary to seek for a temporary base which could be used with safety whilst the submarine obstructions at Scapa were being perfected. The incident that had already occurred at Loch Ewe cast doubt on the safety of that base, since it was unprovided with any obstructions at all and the depth of water made it impossible to improvise them with Fleet resources. Accordingly I looked for other and more easily obstructed ports, and eventually decided on Lough Swilly for the main part of the Fleet, and Loch-na-Keal in the Island of Mull for the ships for which berthing-space could not be found at Lough Swilly. Both ports possessed comparatively narrow entrances, and at Lough Swilly the water was so shallow as to make it difficult for a submarine to enter submerged. It was also a “defended port” and therefore possessed an organisation which would be useful for regulating the entry of ships.