The Fleet then turned to the northward and, owing to a northerly swell, speed had to be reduced on account of the destroyers. During the night the Rosyth force was detached to its base. Speed was increased as the weather improved, and the Scapa and Cromarty forces arrived on the morning of May 31st. The _Iron Duke_ left Scapa for Cromarty during the afternoon of May 31st, and arrived that evening. During the month the procedure of moving squadrons between Scapa and Cromarty was continued. At this period a second line of submarine obstructions, which was designed to prevent the entry of destroyers, as well as submarines, into Scapa Flow, advanced considerably towards completion. Progress was also made with the laying of mine-fields at the entrance. The anchorage at Swarbachs Minn, in the Shetlands, had been selected as a secondary coaling base for the ships of the 10th Cruiser Squadron, and steps were taken to prepare a submarine obstruction for the entrance, and to provide the necessary labour for coaling the ships from colliers. The blockade work of the 10th Cruiser Squadron continued actively during the month, the average number of ships intercepted per week being 62, and the average number sent into port for closer examination, 16. The weather at Scapa during the month was misty, fog being experienced on the 5th, 6th, 21st, 23rd, 24th, 27th and 28th, and snow on the 11th and 12th. The wind during the month was not strong. CHAPTER VIII GERMAN MINES AND SUBMARINES In the early summer of 1915 there was a vague impression in some quarters, unsupported, so far as I am aware, by any confirmatory evidence, that the enemy might exhibit greater activity at sea. But during June, so far as could be ascertained by our intelligence system and by our submarine patrols, the Germans made no attempt to move to sea, but concentrated attention on increased submarine activity. The Grand Fleet, for various reasons unconnected with this development, spent the greater part of the time in harbour, exercising in Scapa Flow, the ships from the Rosyth base being sent up in pairs to exercise and carry out gunnery and torpedo practices. The opportunity of this change of base was usually taken for a searching sweep whilst _en route_ between the bases, so that the North Sea was continually under observation.