At these two ports our enemy was able to maintain a very considerable destroyer force. Its activities were necessarily mainly confined to work in darkness or in thick weather. But in such conditions its efficiency was of a very high order. The public only heard of its activities when it shelled some point of the coast of Kent, or raided our trawlers or other patrols, and, in all conscience, it heard of these activities often enough. Yet we were inclined to suppose them unimportant because their material results were insignificant. The news that a cross-Channel barrage was in course of establishment gave them a new value. But their value to the enemy should not be measured by the casualties they inflicted on our light craft, nor by their occasional excursions into the murder of civilians on shore. It lay in the fact that the enemy’s force permanently withdrew from the anti-submarine campaign numerous destroyer leaders and destroyers which had to be maintained at Dover to cope with it. From Zeebrügge to Emden--the nearest German port--is, roughly, three hundred miles by sea, and it does not need elaborate argument to show that if Zeebrügge and Ostend are permanently out of action the problem of dealing with enemy craft in the narrow seas is totally and entirely changed. With these gone, the East Coast ports became the natural centres from which to command the waters between Great Britain and Holland. They are fifty miles nearer Emden than is Dunkirk. If any German destroyers got west and south of Dunkirk, and the news of their presence were cabled to an East Coast base, destroyers could get between the enemy and his ports without difficulty. Thus, enemy surface craft, based upon German ports, would practically be denied access to Flemish waters altogether, and this by the East Coast and not by the Dover forces. In other words, the Dover patrol forces would, by the closing of Ostend and Zeebrügge, be set free for the highly important work of aiding in the anti-submarine campaign--and there is certainly no naval need that is greater. The strategical objective, therefore, which Admiral Keyes put before himself in his expedition was, so far as he could, to set back the enemy’s naval bases by no less than three hundred miles. Its importance as setting free new forces, both for the direct attack on submarines, and for saving the mine-layers from attack, cannot be exaggerated, for it was a step--and a great step--forward in making sure of the sea communications on which all depends. It must be conceded, then that the results Admiral Keyes had in view amply justify a very considerable expenditure both of material and men. Let us next ask ourselves what kind of material he chose, and how he proposed to use his forces with utmost economy and maximum tactical effect. SIR ROGER KEYES’S TACTICS