If the British were to succeed at all they must succeed quickly. The high ground east of the Salient must be won in a fortnight if they were to move against the German bases in West Flanders and clear the coast. This meant a gamble against the weather, for the Salient was, after Verdun, the most tortured of the Western battlefields. Constant shelling of the low ground west of the ridges had blocked the streams and the natural drainage, and turned it into a sodden wilderness. Weather such as had been experienced the year before on the Somme would make of it a morass where transport could scarcely move, and troops would be exposed to the last degree of misery. Moreover, the "tanks," which had been first used on the Somme the year before, and had done wonders at Arras in breaking through barbed wire and silencing machine-guns, could not be used in deep mud. Whatever might be the strength and skill of the enemy, it was less formidable than the obstacles which nature herself might place in the British path. But the German commanders were no despicable antagonists. In Flanders the nature of the ground did not permit of the kind of defence which they had built on the Somme. Deep dug-outs and concrete trenches were impossible because of the waterlogged soil, and they were compelled to employ new tactics. Their solution was the "pill-box." This was a small concrete fort situated among the ruins of a farm or in some piece of shell-torn woodland, often raised only a yard or two above the ground-level, and bristling with machine-guns. The low entrance was at the rear of the pill-box, which held from eight to forty men. Such forts were easy to make, for the wooden or steel framework could be brought up on any dark night and filled with concrete. They were placed with great skill, and in the barbed-wire defences alleys were left so that an unwary advance would be trapped and exposed to enfilading fire. Their small size made them a difficult mark for heavy guns, and since they were protected by concrete at least 3 feet thick they were impregnable to ordinary field artillery. The enemy’s plan was to hold his first line—which was often a mere string of shell craters—with few men, who would fall back before an assault. He had his guns well behind, so that they would not be captured in the first rush, and would be available for a barrage if his opponents became entangled in the pill-box zone. Lastly, he had his reserves in the second line, ready for the counterstroke before the attack could secure its position. Such tactics were admirably suited to the exposed and contorted ground of the Salient. Any attack would be allowed to make some advance; but if the German plan worked well this advance would be short-lived, and would be dearly paid for. Instead of the cast-iron front of the rest of the battleground, the Flanders line would be highly elastic, but after pressure it would spring back into position with a deadly rebound.