Soon, the operation was so smooth that most keys were obtained in hours and most messages decrypted immediately. The effect of the U.S. bombes on solving the Atlantic U-boat cipher “exceeded all expectations,” noted one internal Navy memo. “Since 13 September 1943, every message in that cipher has been read and since 1 April 1944 the average delay in ‘breaking’ the daily key has been about twelve hours. This means that for the last half of each day, we can read messages to and from Atlantic and Indian Ocean U-boats simultaneously with the enemy. In fact, during these hours the translation of every message sent by a U-boat is at hand about twenty minutes after it was originally transmitted. At present, approximately 15 percent of these keys are solved by the British and the remainder by OP-20-G.”
Once they were broken, the messages would pass to somebody like Janice Martin, a Latin major from the class of 1943 at Goucher, now working in the submarine tracking room, which was located one floor above the bombe deck. Janice, a lawyer’s daughter from Baltimore, was stationed in a room set up so that anyone who opened the door would see, standing in the hallway, a blank wall. Inside, she and her colleagues could see a huge map of the North Atlantic. The broken messages from the M-9 were sent up to her office, translated, typed up by a secretary, handed to the senior watch officer—a man—and then passed to the junior officer, who would be either Janice; her childhood friend Jane Thornton, who had grown up in Baltimore near her and gone through Goucher with her; another Goucher classmate; or a woman from Radcliffe. The U-boats had to report whether they sank an Allied ship or whether any U-boats had been sunk, and the women used these Enigma messages—along with files on individual U-boats and their commanders—to track, with pins, every U-boat and convoy whose location was known. At another desk, several other Goucher women, including Jacqueline Jenkins (later the mother of Bill Nye, aka Bill Nye the Science Guy), tracked “neutral shipping” based on daily position reports. Neutral shipping mattered because if those ships deviated from their assigned sea lanes, it might mean they were surreptitiously supplying U-boats.
In addition to tracking the ships, researchers in Janice’s room would compile a preliminary intelligence report overnight. Between seven thirty and eight a.m., there would be a knock on the door, and Janice’s team would hand over an envelope containing the night’s messages and the report. The messenger would put it in a locked pouch and take it to the Main Navy building downtown. There, a commander named Kenneth Knowles, working with a counterpart tracking room in England, would make decisions about whether to use the intelligence defensively to reroute convoys or offensively to sink the U-boats. The downtown tracking room at first was staffed by enlisted men, but as the war proceeded, WAVES took over there as well. One male officer said the WAVES did a better job because they had had to meet stiffer selection requirements. When the intelligence they generated was passed to the fleet for action, the source of the information was never revealed. By the end of 1943, Janice Martin recalled, “the British turned the whole operation over to us.”
After the carnage of 1942 and early 1943, the Allies had seen a stunning turnaround in the Atlantic. By September 1943, most U-boats had been swept from the Atlantic waters. This was thanks not only to the new high-speed bombes but also to a host of other Allied war measures: advances in radar, sonar, and high-frequency direction finding; more aircraft carriers and long-range aircraft; better convoy systems. The Allies changed their convoy cipher, and D?nitz could no longer read it. The tables turned. During the summer, American hunter-killer units used code breaking along with other intelligence to find and sink big German submarines that were sent out to refuel U-boats. These refuelers were known as milch cows, and between June and August, American carrier planes sank five. In October, they finished off all but one. The refuelers were critical to the U-boats’ ability to stay so far away from their home base, and as the milch cows went down, the U-boats began to drift homeward.
There was always the chance, however, that the U-boats could come back. And they did try. In October 1943, the U-boats reappeared. But now the costs were punishingly high. For every Allied merchant vessel sunk, seven U-boats were lost. Now D?nitz was the one who could not build boats fast enough to replace those he was losing. In November, thirty U-boats ventured into the North Atlantic and sank nothing. The U-boats began lurking elsewhere, clustering around the coast of Britain, hoping to intercept materiel brought in for an anticipated invasion of France. D?nitz was always trying to innovate the U-boats, adding a Schnorchel that enabled them to remain submerged longer. He was willing to sacrifice his boats, and his men, and kept the U-boats in the water even as a way to tie up Allied resources.
But it was a losing battle. In May 1944, the Allies sank half the U-boats in operation—more than the Germans could replace. More than three-quarters of the U-boat crews were killed, suffering terrible watery deaths. The women in the tracking room were privy to the full immensity and horror.
By now the British had indeed handed over the four-rotor bombe operations to the Americans. After the war, a U.S. Navy file was made of messages from grateful—and gracious—British colleagues. “Congratulations from Hut six on colossal… week,” said one missive from Bletchley. An internal British memo acknowledged that “by half way through 1944” the Americans “had taken complete control of Shark and undoubtedly knew far more about the key than we did.”
The Germans found other uses for the Enigma, which achieved less fame but were extremely dramatic. From June 1943 to the summer of 1944, the Nazis attempted to use submarines to run Allied blockades and travel between Europe and Japan, to load up on supplies to feed the war effort. Special Enigma keys were devised for use by both the Germans and the Japanese, and other ciphers also were employed.