He told Wilhelm that if submarine crews were to maintain their daring—their “ardor”—they needed full assurance that they would not be abandoned if they encountered difficulties. “To us,” Scheer declared, “every U-boat is of such importance, that it is worth risking the whole available Fleet to afford it assistance and support.”
By this point, Germany’s U-boat fleet had achieved a level of strength that at last gave it the potential to become a truly imposing force. Where in May 1915 the navy had only thirty U-boats, by 1917 it had more than one hundred, many larger and more powerful than Schwieger’s U-20 and carrying more torpedoes. With this robust new fleet now ready, the pressure to deploy it to the fullest grew steadily.
A German admiral, Henning von Holtzendorff, came up with a plan so irresistible it succeeded in bringing agreement between supporters and opponents of unrestricted warfare. By turning Germany’s U-boats loose, and allowing their captains to sink every vessel that entered the “war zone,” Holtzendorff proposed to end the war in six months. Not five, not seven, but six. He calculated that for the plan to succeed, it had to begin on February 1, 1917, not a day later. Whether or not the campaign drew America into the war didn’t matter, he argued, for the war would be over before American forces could be mobilized. The plan, like its territorial equivalent, the Schlieffen plan, was a model of methodical German thinking, though no one seemed to recognize that it too embodied a large measure of self-delusion. Holtzendorff bragged, “I guarantee upon my word as a naval officer that no American will set foot on the Continent!”
Germany’s top civilian and military leaders converged on Kaiser Wilhelm’s castle at Pless on January 8, 1917, to consider the plan, and the next evening Wilhelm, in his role as supreme military commander, signed an order to put it into action, a decision that would prove one of the most fateful of the war. On January 16, the German Foreign Office sent an announcement of the new campaign to Ambassador Bernstorff in Washington, with instructions that he deliver it to Secretary Lansing on January 31, the day before the new campaign was to begin. The timing was an affront to Wilson: it left no opportunity for protest or negotiation and came even as Bernstorff was promoting the idea that Germany really did want peace.
Wilson was outraged but chose not to see the declaration itself as sufficient justification for war. What he did not yet know was that there was a second, very secret message appended to the telegram Bernstorff had received and that both telegrams had been intercepted and relayed to Blinker Hall’s intelligence division in the Old Admiralty Building in London, which by now oversaw a second, and singularly sensitive, component of Room 40’s operations—the interception of diplomatic communications, both German and, incidentally, American.
THE FIRST OF Hall’s men to grasp the importance of the second telegram was one of his top code breakers, Lt. Cdr. Nigel de Grey. On the morning of January 17, 1917, a Wednesday, Hall and another colleague were attending to routine matters, when de Grey walked into the office.
“D.I.D.,” he began—using the acronym for Director of Intelligence Division—“d’you want to bring America into the war?”
“Yes, my boy,” Hall answered. “Why?”
De Grey told him that a message had come in that was “rather astonishing.” It had been intercepted the day before, and de Grey had not yet managed to read the entire text, but what he had deciphered thus far seemed almost too far-fetched to be plausible.
Hall read the partial decrypt three or four times, in silence. “I do not remember a time when I was more excited,” he wrote.
But just as quickly, he realized that the remarkable nature of the message presented a challenge. To disclose the text right away would not only put the secret of Room 40 at risk but also raise questions about the credibility of the message, for what it proposed was certain to raise skepticism.
The telegram was from Germany’s foreign secretary, Arthur Zimmermann, written in a new code that was unfamiliar to Room 40. The process of rendering its text in coherent English was slow and difficult, but gradually the essential elements of the message came into view, like a photograph in a darkroom bath. It instructed Germany’s ambassador in Mexico to offer Mexican president Venustiano Carranza an alliance, to take effect if the new submarine campaign drew America into the war. “Make war together,” Zimmermann proposed. “Make peace together.” In return, Germany would take measures to help Mexico seize previously held lands—“lost territory”—in Texas, New Mexico, and Arizona.