On October 21st a submarine was reported just outside Cromarty by an armed trawler, and another report was received of one having been sighted by the destroyer _Lynx_. The submarine obstruction at Cromarty, designed by Captain Munro, had now been completed, and the base was considered secure. It would, however, only accommodate a small portion of the Fleet. The dispositions given above were maintained until October 22nd, when the _Iron Duke_, 1st and 4th Battle Squadrons, the _Active_ and two divisions of destroyers of the 2nd Flotilla, arrived at Lough Swilly. The 3rd and 6th Battle Squadrons and 2nd Cruiser Squadron took their place to the north-westward of the Hebrides as an outer blockade line and support for the cruiser squadrons. The 2nd Battle Cruiser Squadron and four destroyers were detached to the southern part of the North Sea on the 23rd to support the Commodore (T) in carrying out aerial operations in the Heligoland Bight. The operations failed owing to the difficulty the sea-planes experienced in rising off the water, and the 2nd Battle Cruiser Squadron returned to Cromarty. On arrival of the 1st and 4th Battle Squadrons at Lough Swilly, steps were immediately taken to lay an anti-submarine obstruction at the entrance, and this was very smartly completed with the limited resources of the squadrons by 4 P.M. on the 23rd, and for the first time since the declaration of war the Fleet occupied a secure base. Wire hawsers provided by the ships of the Fleet were suspended at varying depths between six colliers which were anchored across the entrance, with target rafts as intermediate supports. It was a fairly effective obstruction, and armed steamboats from the fleet patrolled near it with destroyers as a support. The relief to those responsible for the safety of the Fleet was immense, and attention was at once turned to the well-being of the personnel, which had been pressed very hard, and to improving the efficiency of the ships in gunnery and torpedo work. Battle practice targets were ordered over from Lamlash, in the Island of Arran, a pre-War practice base, with the intention of carrying out practice in the waters north-west of Ireland. The work of retubing the condensers of the _Iron Duke_ was once more taken in hand, and ships were given the opportunity of overhauling and adjusting machinery, steam being put back to longer notice than had previously been possible. The anti-submarine defence was continually strengthened and improved during the stay of the Fleet, and the colliers supporting it were gradually replaced by trawlers and drifters. In order to give the men some much-needed diversion and exercise a pulling regatta was organised and held on October 26th, and the men were landed for route marches as frequently as possible during the stay of the ships at Lough Swilly.