On land, novel factors in the war had created a dilemma that stood for years beyond the ability of military leaders to solve. Machine guns, barbed wire, and modem transportation networks combined to form a defensive system that an advancing enemy could not break through; indeed, attempts to do so led to hideous casualties. A lack of imagination on the part of the generals combined with an absence of effective countertechnology and a failure of will on the part of political leaders to produce prolonged catastrophe. In contrast to that grim record, the Allies, led by Britain, were able to devise a successful response—and in a timely way—to the threat of the submarine. As on land, military conservatism at the highest levels stood in the way of an effective solution, but,, in the end, a new generation of navy leadership emerged that proved less hidebound than the military brass in adapting to the new technology of war. The first hint of severe crisis came in the fall of 1 9 1 6. The German navy had failed to alter the balance of power in the North Sea when it met the British Grand Fleet at Jutland. Now, within a few months, the authorities in Berlin turned to an intensified form of submarine warfare against merchant vessels. Some restrictions remained, but the upward trend in Allied losses suggested what a potent weapon the submarine might become. In October 1916, for example, German submarines sank 175,000 tons of Allied shipping, af)eak so far in the war. Britain stood as the chief target of the submarine offensive. Since the last decades of the nineteenth century, there had been a steady rise in the amount of food the country needed to import from abroad. By the start of the war, fully 80 percent of the bread consumed, along with vast quantities of other foods, came from foreign sources. An.effective submarine blockade promised to drive Britain quickly to the brink of starvation. Apart from Britain's food needs, the nation's war effort, from shipping armies to France to supporting far-flung operations from the eastern Medi terranean to the Persian Gulf, depended upon an unbroken stream of merchant traffic. Statistical analysis showed the German High Command that Britain could be knocked out of the war within six months if German submarines disrupted the island nation's sea traffic. The Germans hoped to destroy 600,000 tons of British shipping per month. Neutral countries like Norway whose ships played a crucial role in the carrying trade with Britain would become too frightened to continue.