THE deterioration of the French army made it essential that the British should engage in a vigorous, and as far as possible an uninterrupted, summer campaign. The extreme danger of the submarine campaign dictated its direction against the Belgian ports, the closest and most infested 'nests of destruction'.1 Yet it was impossible to break out coastwards from the Ypres salient until the right had been secured. South-west of the city the German defences were thrust forward on the Wytschaete--Messines ridge. The good observation gained therefrom enabled the British lines to be enfiladed, and even taken from the rear, for several miles to the north. The ridge extends for about eight miles, and is nowhere more than 200 feet high, but has, in places, an abrupt and dominating face towards the west. By the end of April the German command realized that an attack here was imminent; and if Rupprecht had had his way the position would have been evacuated. The Arras battle had taught him that commanding positions, where the defences can be easily picked up, were much more difficult to maintain against a superior artillery than inconspicuous lines carefully drawn in featureless country. Moreover, his guns were inconveniently crowded in forward positions round Messines, and he correctly anticipated that a large proportion would be disabled in the preliminary bombardment. Faced, however, by a unanimous protest from the local commanders, he lacked the strength of will to persist.
The battle of Messines proved in effect one of the most complete local victories of the war. It was the kind of victory that required immense and lengthy preparation. Its most essential and devastating feature, the mine-____________________