Shortly after my taking up the post of First Sea Lord at the Admiralty, at the end of 1916, the question was discussed once more.  At that time the danger of attack by enemy raiders on shipping in the North Atlantic was small; the protection needed was against attack by submarines, and the dangerous area commenced some 300-400 miles from the British Islands.  It was known that unrestricted submarine warfare was about to commence, and that this would mean that shipping would usually be subjected to torpedo attack from submarines when in a submerged condition.  Against this form of attack the gun armament of cruisers or armed merchant ships was practically useless, and, however powerfully armed, ships of this type were themselves in peril of being torpedoed.  Small vessels of shallow draught, possessing high speed, offered the only practicable form of protection.  Shallow draught was necessary in order that the protecting vessels should themselves be comparatively immune from successful torpedo fire, and speed was essential for offensive operations against the submarines.

Convoy sailing was, as has been stated, the recognized method of trade protection in the old wars, and this was a strong argument in favour of its adoption in the late war.  It should, however, be clearly understood that the conditions had entirely changed.  Convoy sailing for the protection of merchant ships against torpedo attack by submarines was quite a different matter from such a system as a preventive against attack by surface vessels and involved far greater difficulties.  In the days of sailing ships especially, accurate station keeping was not very necessary, and the ships comprising the convoy sailed in loose order and covered a considerable area of water.  On a strange vessel, also a sailing vessel, being sighted, the protecting frigate or frigates would proceed to investigate her character, whilst the ships composing the convoy closed in towards one another or steered a course that would take them out of danger.

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