The staggering losses of April evoked a decisive sense of urgency in people who could make a difference. In his memoirs, written in the 1930s, Lloyd George put his personal intervention at the center of the change. Indeed, on April 30, he made a well-publicized visit to the Admiralty to investigate the situation and presumably to push for the adoption of a convoy policy. The appearance of the prime minister in this dramatic fashion had less of an impact than he claimed. For one thing, the situation had become so critical by the middle of April that naval authorities like Duff had already begun to adopt the convoy system. Moreover, employing convoys in an efficient, effective, and widespread way had to wait until summer 1917. The most promising results were evident only in the fall. Unenthusiastic commanders and the lethargic practices of the naval bureaucracy continued to delay things well beyond Lloyd George's dramatic drop-by. One element that promoted convoys was the initiative of relatively junior officers. Individuals like Captain Herbert Richmond and Commander Reginald Henderson committed themselves to the adoption of the convoy, and they provided civilian leaders like Lloyd George with the information needed to overcome the military conservatives. For example, hidebound admirals had argued that the number of ships traveling to and from British ports each week was so great that they could never be properly escorted. Henderson demon strated—and informed Lloyd George—that the calculations were faulty. They should have been based only on the number of ocean-going ships, discounting voyages by small coastal vessels. By that standard, the current percentage of losses was appalling. On the other hand, the number of escorts available would be adequate to protect these imperiled ships. The success of relatively junior naval officers in convincing key political leaders to adopt a winning strategy had no counterpart, of course, in land operations. The discipline in both services militated against such detours around the chain of command; but naval men took the risk, while their comrades in the army did not. A partial explanation can be found in the solutions offered. Officers like Richmond and Henderson could point to an old and traditional tool of warfare merely waiting to be adopted. The objections of senior admirals that sea traffic around the British Isles was too extensive to be put into convoys could be refuted easily. Knowledgeable naval men had the facts and figures they needed in hand. On land, there was no such packaged solution available. Officers could point to the promise — still basically untested—of the tank, but its early trials on the battlefield hardly made it a convincing solution to the blood-soaked stalemate. The strongest tribute to the success of the convoy came from the opposing side in the words of Admiral Karl Doenitz, a submarine officer in World War I, then commander of the German U-boats from 1936 to 1943, and leader of the German navy from 1943 to the end of World War IL As he put it in his memoirs, "The German U-boat arm achieved great success; but the introduction of the convoy system in 1917 robbed it of its opportunity to become a decisive factor."