Practice at rocks or small islands was next resorted to, but no really suitable rocks existed, and, in any case, practice at them eventually involved too much risk of submarine attack, as the German submarines began to find their way to the westward of Scotland. Towards the end of 1915 it became possible, owing to the increase in the number of destroyers attached to the Fleet, and to the provision of submarine obstructions at Cromarty, to carry out gunnery practices at long ranges at targets in the Moray Firth, and real improvement dated from that period. Later still, battle practice targets were brought to Scapa Flow, and the long-range firing was carried out in the Pentland Firth, a still more convenient place. Meanwhile Scapa Flow itself had been developed for all the preliminary gunnery practices which could be carried out with guns up to 6-inch in calibre, and also for night firing and for torpedo work. The fine stretch of water was secure from submarine attack after the obstructions had been provided, and ships could practise by day and night without danger of attack. The Flow was simply invaluable for this purpose. Ships were firing, running torpedoes, practising fire control exercises, carrying out experiments and exercising in dealing with attacks by destroyers, day after day, from daylight until dark. After dark, night firing was frequently carried out, and occasionally a division of battleships was exercised in steaming in company, without lights, in order to give the officers of watches practice. When the constant sea work of the earlier months of the War gave place to occasional cruises, the seagoing and fighting efficiency of the Fleet was maintained at a remarkably high standard as a result of the work in Scapa Flow. During the period 1914–16 a marked advance was undoubtedly made in gunnery efficiency. At an early period of the War a memorandum was issued pointing out the necessity for increased attention to drill and organisation. Absolute perfection was insisted upon, and it was obtained, by the strenuous efforts of officers and men. I knew that we had to deal with an enemy who would be as perfect as constant drill could ensure. A great extension of the system of Director Firing, by which one officer or man could lay and fire all the guns, was made. The situation in this respect before the War was that a few ships had been fitted for the system, which had been devised by Admiral Sir Percy Scott. But a very large number of officers were sceptical as to its value compared with the alternative system; there was considerable opposition to it, and the great majority of the ships were not fitted. In some cases the system was not favoured even in the ships provided with it.