For the Allies, 1942 marked the low point in the Battle of the Atlantic. In the last six months of that year, German U-boats sank nearly five hundred Allied ships as they tried to make the crossing between North America and England, destroying 2.6 million tons of shipping. Now 1943 was shaping up to be worse. March 1943 had been the most terrible month of the whole war, with ninety-five Allied merchant ships sunk by Nazi submarines. In one major convoy attack, the U-boats sank dozens of ships in just three days.
The American war machine, as mighty as it was, could not produce enough ships to make up for such heavy losses. The U-boat situation had always been a crisis, but now the crisis was acute. England needed wheat and other food supplies. Joseph Stalin needed weapons to drive the Germans out of the Russian heartland. And the Allies needed to sweep the Atlantic Ocean clear of the U-boat menace once and for all, if they were ever to make the waters safe for the vast lines of convoys that would be needed to transport troops and tanks and weapons in sufficient numbers to mount—at long last—an Allied invasion of France.
The British still had charge of code-breaking efforts in the Atlantic theater. But the Americans were becoming more than just a junior partner. It had taken a while for the two services to begin working smoothly together. Agnes Driscoll’s early rebuff of the British had set the Allied relationship back in 1941, but beyond the recalcitrance of a single woman, the British Navy had been appalled by the amateurish nature of the U.S. Navy’s overall intelligence operation. The British would share reports that were never responded to, possibly never received by the people who needed to see them. The United States, in return, felt their English friends were withholding details about the Enigma project. Both services were right: U.S. naval intelligence had been dysfunctional at the outset, and the British were indeed holding back. Part of their secretiveness sprang from a desire to ensure that the “special intelligence” produced by the Enigma code-breaking project was used only defensively, to reroute Allied convoys into safe waters. They feared if the more aggressive Americans used Enigma offensively, to sink U-boats, this would tip off the Germans that the cipher had been broken.
But an accord was reached over time, and secure lines set up between American and British naval intelligence, as both services worked hard to track the U-boats and predict their movements. The effort at no time was easy, but it became excruciatingly difficult after February 1942, when the German subs started using the four-rotor naval Enigma, and Allied efforts against it proved mostly futile. During this dark period the Allies struggled to predict U-boat movements using methods such as high-frequency direction finding, or HF/DF, which was a way of locating subs using their radio signals. The Allied tracking rooms availed themselves of every form of intelligence—HF/DF, news of sinkings and sightings—to locate the submarines and route the convoys to dodge them. But the impenetrability of the four-rotor Enigma kept them at a major disadvantage until, in late October 1942, four British destroyers patrolling the eastern Mediterranean targeted and attacked a U-boat, the U-559. The submarine, which had surfaced, began to sink, and a group of British sailors tore off their clothes, dove into the water, and swam over to it, to retrieve papers and equipment. Two of the sailors, an officer and a seaman, were coming up a ladder when a rush of incoming water overcame them, and they went down with the sub. The others were able to scramble into a whaler. The men had retrieved two books, one of them a weather cipher book giving current key settings, which found its way to Bletchley Park and helped the code breakers get into the four-rotor Enigma cipher. They broke Shark for the first time using the bombe, to find a message showing the position of fifteen U-boats. They were back in.
Even with this assistance, though, the Allied ability to break the Enigma ciphers was spotty. Cipher books changed, and often the Allied code breakers had to try to come up with the key using hand methods. The British bombe machines could not help. Because the extra, fourth, rotor created twenty-six times more ways to encipher each letter, the older British bombes would have to run twenty-six times faster, or there would have to be twenty-six times more of them, to test every possibility.
What was needed, to attack the naval Enigma, was a bombe much faster than the ones being run in England. Allied officials decided that America—which had more factories, more raw material, more engineers and mathematicians—would build scores, maybe even hundreds, of high-speed machines capable of handling the four-rotor Enigma cipher. The Navy engaged Joseph Desch, the Dayton inventor, to design an American bombe. Desch was an inspired choice. A graduate of the University of Dayton, he did not boast an Ivy League education or even a PhD. What he had was an engineer’s genius, the ability to work with his hands, and real-life experience in how a factory floor functioned.
Raised and schooled in Dayton—an excellent proving ground for a kid with inventive instincts—Desch as a boy had been fascinated by electronics and ordered vacuum tubes from a mail-order company that sent him the supplies he wanted, assuming he was an adult. Early in his career he worked at Telecom Laboratories, founded by Charles Kettering, and then at Frigidaire. Moving to National Cash Register, he and his staff patented the first electronic accounting machine. Desch also designed a new type of vacuum tube he made by hand. The renowned MIT engineer Vannevar Bush, doing war-related work through his National Defense Research Committee, admired Desch and brought him to the attention of the right people. A plan was drawn up: Desch would design a high-speed bombe, working with Navy engineers and mathematicians. The machine would be built by Navy mechanics and NCR employees who had the requisite clearances. The Navy women—though they did not know it—had been brought to Dayton to wire thousands of “commutator wheels” to go on the front of the American bombe machine, fast-spinning wheels to test possible settings.
In short: What the Americans were going to produce was the very roomful of high-powered machines that the Germans thought could never be built.