Diagrams of submarine screens were, therefore, drawn up to meet the different conditions resulting from the presence of varying numbers of destroyers, or a decreased number of ships requiring to be screened, and also providing for the ships being in various formations. In November, 1916, the number of these diagrams was seventeen. Early in the War the danger of successful submarine attack on warships at sea, whether in company or proceeding singly, had impressed on us the necessity of taking every precaution for safety, and the practice of the fleet steering zigzag courses was devised and generally adopted in accordance with my directions. In the case of a fleet or squadron, the usual practice was to carry out the alterations of course by turning the ships together; occasionally the turn was made “in succession,” but this was exceptional. In small squadrons, the turns were occasionally made at fixed time intervals without signal. Zigzagging had a very beneficial effect on the manner in which officers of watches kept station in a fleet, since there is no better practice than keeping station on a line of bearing, a far more difficult matter to the novice than keeping station astern of another ship. I attribute the excellent manner in which the ships were handled in 1915 and 1916 very largely to this early experience. Much theoretical investigation was instituted to determine the method of zigzagging, both in a fleet and in a single ship, which gave the greatest protection against submarine attack, and actual experiments took place with our own submarines with a view to forming correct conclusions; the flag officers of the fleet rendered me much assistance in this as in all other matters. The experience of the Grand Fleet was utilised in the instructions subsequently issued to merchant ships, and the value of zigzagging in reducing the danger of submarine attack was clearly shown during the year 1917 by the comparative immunity of merchant ships that complied with the orders as compared with those that did not do so. Occasionally, of course, zigzagging brought a ship into danger, but this was exceptional as compared with the general immunity given. When the convoying of merchant ships through the submarine zone was instituted in 1917, after I had returned to the Admiralty, the Grand Fleet experience was again of value in the preparation of instructions. The supremely important question of how best to handle in action the large and increasing Fleet engaged my attention from the commencement. In drawing up the various instructions for the conduct of the Fleet, both when cruising and in action, I availed myself of the advice and assistance of the experienced flag officers commanding the various Squadrons. Much discussion took place on these matters, and many of the dispositions adopted formed the subject of actual experiment at sea before being incorporated in the orders.