At first unrestricted submarine warfare seemed likely to achieve all the results the German navy had promised. Their target had been to sink 600,000 tons of shipping a month, doubling the previous rate. They reached it in March. In April they went on to sink 869,000 tons. There they peaked. Sinkings hovered around the 600,000 ton mark all summer, were down to 500,000 tons in August, and by the end of the year had fallen to 300,000 tons. Why?
The most obvious reason was the introduction of convoys, a system that the Admiralty had declared impracticable since, among other reasons, it believed that it did not have enough destroyers to escort the amount of shipping involved. Since it included all coast-wise shipping in its calculations, it was proved badly wrong, and when, at the insistence of Lloyd George, convoys were introduced at the beginning of April, their success was immediate. Once the Americans began to make their weight felt, they were able not only to reinforce convoy protection but to build merchant vessels faster than submarines could sink them.
The Germans had also miscalculated the cargo space available to the Allies, the degree of British dependence on grain imports, and above all the British capacity for countermeasures in the form of commerce control and commodity allocation through rationing. The British government indeed operated a siege economy so successfully that by the end of 1917 its grain reserves had actually doubled.
None of this, however, was apparent in the summer of 1917, when the population of London was subjected to yet another ordeal: daylight bombing from the air. The importance of air power had not been underestimated by any of the belligerents before 1914. For ten years previously imaginative fiction had depicted the horrors of air bombardment of cities by aircraft that had yet to be invented, but the military themselves were more concerned with the effect of aircraft on surface warfare—in particular their capacity to carry out the reconnaissance operations that could no longer be undertaken by cavalry. But, since such reconnaissance was possible only if uninterrupted by enemy aircraft, the main function of the air arm rapidly became to establish command of the air over the battlefield, whether by direct air combat or by destruction of enemy airfields. In single combat between air aces above the mud of the trenches, the traditional romance of war enjoyed a very brief revival.
‘Strategic bombardment’, attack on the civil resources of the enemy, was slower to develop. German dirigible balloons, named after their chief sponsor the Graf von Zeppelin, had attacked Antwerp in August 1914 (British aircraft responded against Zeppelin sheds in Düsseldorf in October) and began night raids on the United Kingdom the following January. But their navigation was too inaccurate and their destructive power too slight for these raids to be more than a dramatic nuisance; one, however, that provided propagandists with further evidence of German ‘frightfulness’. By 1917 more reliable long-range aircraft had been developed, and that summer German Gotha bombers carried out daylight raids on London. The physical damage and casualties were slight but the moral effect was enormous.
Against the advice of the military, who needed all the resources they could get for the war in France, an Independent Air Force was formed, based in eastern France, with the task of retaliating against German territory. Since the only targets within range were the towns of the upper Rhine the immediate impact of these operations was negligible, but in the long run their implications were far-reaching. On the very inadequate evidence of their success the newly formed Royal Air Force was to build a doctrine of strategic bombing that would dominate British and later American strategic thinking for the rest of the twentieth century.