In the circumstances with which we were dealing in 1917 the requirements were quite otherwise. It was essential for the protection of the convoy that the ships should keep close and accurate station and should be able to manoeuvre by signal. Close station was enjoined by the necessity of reducing the area covered by the convoy; accurate station was required to ensure safety from collision and freedom of manoeuvre. It will be realized that a convoy comprising twenty to thirty vessels occupies considerable space, even when steaming in the usual formation of four, five or six columns. Since the number of destroyers or sloops that could be provided for screening the convoy from torpedo attack by submarines was bound to be very limited under any conditions, it was essential that the columns of ships should be as short as possible; in other words, that the ships should follow one another at close intervals, so that the destroyers on each side of the convoy should be able as far as possible to guard it from attack by submarines working from the flank, and that they should be able with great rapidity to counter-attack a submarine with depth charges should a periscope be sighted for a brief moment above the surface, or the track of a torpedo be seen. In fact, it was necessary, if the protection of a convoy was to be real protection, that the ships composing the convoy should be handled in a manner that approached the handling of battleships in a squadron. The diagram on p. 107 shows an ideal convoy with six destroyers protecting it, disposed in the manner ordered at the start of the convoy system. [Illustration on page 107, with caption "Diagram illustrating a convoy of 25 Merchant Ships, with an escort of 6 Destroyers zigzagging at high speed for protection. The convoy shown in close order and on its normal course."] [Illustration on page 108 shows, according to its caption, "Typical convoy and escort of 10 Trawlers in the early days of convoy."] How far this ideal was attainable was a matter of doubt. Prior to 1917 our experience of merchant ships sailing in company had been confined to troop transports. These vessels were well officered and well manned, carried experienced engine-room staffs, were capable of attaining moderate speeds, and were generally not comparable to ordinary cargo vessels, many of which were of very slow speed, and possessed a large proportion of officers and men of limited sea experience, owing to the very considerable personnel of the Mercantile Marine which had joined the Royal Naval Reserve and was serving in the Fleet or in patrol craft. Moreover, even the troop transports had not crossed the submarine zone in company, but had been escorted independently; and many naval officers who had been in charge of convoys, when questioned, were not convinced that sailing in convoy under the conditions mentioned above was a feasible proposition, nor, moreover, were the masters of the transports.