Hunt and Kill

by Theodore P. Savas

  When Germany invaded Poland in 1939, Rejewski and several colleagues escaped the country. News of their work eventually reached the Allies. Britain and the United States advanced Rejewski’s efforts and built more advanced “bombes,” as they were called in English, using them for the duration of the war.90 By the spring of 1941, the British Tabulating Machine Company had delivered eight bombes to GCCS at Bletchley Park; that number rose to 12 by the end of the year.91

  Foreign Material Exploitation and Enigma

  The Royal Navy assisted Bletchley Park both inadvertently and intentionally. The sinking of Kptlt. Hans-Wilhelm von Dresky’s U-33 by the minesweeper HMS Gleaner on February 12, 1940, yielded three Enigma rotors from the pockets of a German seaman who had forgotten to throw them overboard. Two of the rotors, known as VI and VII, were previously unknown to GCCS.92 Three weeks later the converted whaler Krebs fired on a Royal Navy task force, which proceeded to run the German ship aground. A boarding party from HMS Somali collected two rotors and the Enigma keys for February. Analysis yielded February, April, and some May Enigma traffic, and also demonstrated naval Enigma could be broken—even in the months before British bombes began operating.93

  On April 26, 1940, a boarding party from the destroyer HMS Griffin captured a 394-ton German “fishing trawler” armed with torpedoes. Before the party could board, however, a German crewman threw two canvas bags overboard, one of which was recovered by a British gunner. The bag held naval Enigma keys for April 23-26, providing the codebreakers at Bletchley Park another break into naval Enigma.94

  Harry Hinsley, a traffic analysis expert assigned to Bletchley Park’s Hut 8, realized Germany needed weather information for air operations and planning, and that the Kriegsmarine stationed ships in the North Atlantic to observe and report the weather.95 Hinsley suggested the Royal Navy send a task group to capture a weather ship, hoping it could be taken before its crew could send a distress call. The subsequent capture of München on May 7, 1941, yielded the Short Weather Cipher and the inner and outer Enigma settings for the Home Waters keys for June.96 A repeat mission succeeded with the capture of the trawler Lauenburg on June 28, 1941, which yielded the July home waters key, Stecker (plugboard) settings, and a sheet of internal settings.97

  The chance capture of Kptlt. Fritz-Julius Lemp’s U-110 off Iceland just two days after the capture of München (during which Lemp was killed under circumstances yet to be fully understood or univerally accepted) yielded a bonanza of codebooks, instructions, key lists, an Enigma machine, and all eight rotors then in use by the Kriegsmarine. 98 This capture reduced the Enigma solution time for June from eleven days to an average of just six hours.99 This new ability to read Enigma traffic lasted until the introduction of four-rotor Enigma on February 1, 1942, the beginning of an Enigma “blackout” that would last until December 1942.100

  The final capture of note in the Enigma story took place on October 23, 1942, when several escorts and an aircraft depth charged and crippled Kptlt. Hans Heidtmann’s U-559 in the Mediterranean. A three-man boarding party from HMS Petard climbed onto the heavily damaged submarine and removed the current edition of the short signal book for weather reports, as well as the short signal book for reporting enemy ships, battle results, and other tactical information. The U-boat sank with two of the men still aboard.101 The weather codebook gave Bletchley Park cribs that would be useful in the solution of four-rotor Enigma. By the time this edition of the codebook expired, Hut 8 had developed a method of taking cribs from the tactical short signal book. This method was used until the end of the war.102

  Four-rotor Enigma

  The Enigma blackout began with the introduction of four-rotor Enigma on February 1, 1942. The fourth wheel theoretically introduced a multiple of 26 into the solution time for Enigma, requiring either 26 times as many bombes or a bombe which would run 26 times as fast as the existing British bombe.103

  However, many three-rotor Enigma machines remained in use, and Bletchley Park’s analysis of four-rotor Enigma messages eventually showed that four-rotor Enigma keys were identical to three-rotor keys, with only the fourth rotor setting being different. Therefore, once a three-rotor solution was found, only 26 tests were required to determine the position of the fourth rotor. Successful solutions based on this principle reduced the number of ships sunk in convoy in January and February 1943 by fully one-half when compared to November and December of 1942.104

  Development of the American Bombe

  The Enigma problem assumed critical importance to the U.S. Navy when the United States entered the war in December 1941. Although Bletchley Park had promised their American counterparts a bombe, they were unable to produce a workable high-speed machine. Therefore, Commander Joseph Wenger, deputy chief of OP-20-G, “felt obliged to recommend to higher authority that we take the matter in our own hands and proceed as we felt proper.”105

  The urgency of the U-boat situation in the Atlantic, coupled with the failure to receive any equipment or reassurance from the British, led to a development contract between the U.S. Navy and the National Cash Register Machine Company (NCR). The contract, signed on September 4, 1942, committed the parties to research and development of “an extremely high-speed cipher machine of the Enigma type.”106 Two months later on November 11, 1942, letters from the Vice Chief of Naval Operations to the Chief of Naval Personnel (via the Chief of the Bureau of Ships) and the Commandant of the Ninth Naval District established the U.S. Naval Computing Machine Laboratory (or NCML) to assist NCR in the production of bombes and the training of personnel.107 The Navy located NCML at NCR’s plant in Dayton, Ohio, under the direct control of OP-20-G with funding from the Bureau of Ships.108

  Everyone associated with the bombe project understood it to be a gamble, both because of its technical difficulty and because of the possibility that German changes to equipment or procedures might render their hard work useless. They were also aware that while the high-speed bombes would theoretically work, practical engineering had not yet caught up with theory. Also, Bletchley Park had expressed doubts about the success of the project, as the American plan was “at variance with British experience and recommendations.”109

  Shortages of critical materials also affected the bombe project. The Radio Division of the Bureau of Ships indicated that “serious difficulties were being experienced in getting certain critical materials necessary in radio manufacture,” many of which were required in bombe construction.110 Because of the material shortages, project officers had to decide whether to delay production until a high-speed commutator (a critical component in the bombe’s operation) became available. Against the advice of the engineers, the officers decided to start construction before receiving any commutators. The gamble worked when commutators arrived in time to be installed in the first bombes.111

  Discussions with the British led to the decision early in 1943 to build 96 bombes, a number that eventually grew to 120.112 To assist in the construction of bombes, the Navy sent 600 newly inducted Waves and 200 men to Dayton, where they worked in Building 26 of the NCR plant. As the first bombes were completed, the sailors and Waves began training to operate and maintain the new machines.113 Navy bombes were large and heavy machines—seven feet tall, two feet wide, 10 feet long, and 5,000 pounds. Both the front and the back sides contained eight columns of four commutators, also known as “rotors” or “wheels.” The top wheel of each column corresponded to the fourth rotor of the Enigma machine, while the bottom rotor represented the rightmost rotor of the Enigma. The bottom wheel spun at 1,725 revolutions per minute, allowing the bombe to complete a “run” in 20 minutes.114

  U.S. Bombes in Operation

  On May 28, 1943, the first two prototype bombes, known as “Adam” and “Eve,” were put into operation at U.S. Naval Computing Machine Laboratory.115 The first production bombes followed that August.116 Secure communications were set up between Dayton and Washington, and the bombes were operated in Ohio for the first few months to remain within easy reach o
f the maintenance and design engineers.117 When the new “Laboratory Building” at the Naval Communications Annex was completed in September 1943, four bombes per week were shipped to Washington.118

  Bombe menus were made up by cryptanalysts on site and sent to the Laboratory Building by pneumatic tube. The bombe operator, always a Wave, used a menu to set up the machine, with help from a supervisor.119 The operator started the machine and monitored its operation for the twenty minutes required for a run. As the bombe sped through every possible rotor setting, it would stop just long enough to print the rotor settings that met the conditions required by the menu (also called “hits”). When the run was complete the operator gave the printout to her supervisor. The supervisor checked the results on an M-9 machine, known appropriately as a “checker,” which verified the results of the bombe run and permitted the supervisor to determine any unknown Stecker settings. The supervisor took this complete and verified solution to the watch officer.120 The solution, known as a “story,” was logged and sent to the cryptanalysts via the pneumatic tube.121

  By the end of 1943, 77 bombes were operating continuously at the Annex. OP-20-G and NCML kept pace with German changes to their communication procedures, and by the time U-505 was captured in early June 1944, a collection of 96 bombes routinely broke U-boat message traffic with an average delay of 12 hours from the time the message was intercepted.122

  Producing and Using Ultra Intelligence

  The Waves used M-9 machines to decrypt short messages. Longer messages were transferred to paper tape and run through an M-8, a converted Navy cipher machine containing rotors wired to match those of the Enigma machine. Linguists in another section of OP-20-G translated the German text into English.123 Watch officers from F-211, the “Secret Room,” read the intercepts as they arrived at COMINCH and made sure the information was posted on U-boat and convoy maps.124

  The U.S. Navy began using Ultra intelligence offensively at approximately the same time “Adam” and “Eve” began operations (May 1943), although much of the Ultra at that time came from Bletchley Park. Early in June 1943, aircraft from the carrier USS Bogue sank two U-boats with the aid of Ultra. Between January 1943 and the end of the war, U.S. naval forces sank 54 U-boats with direct assistance from Ultra intelligence; approximately 30 more were sent to the bottom with the indirect aid of Ultra.125

  Human Intelligence

  The majority of human intelligence (HUMINT) relevant to the capture of U-505 came through the interrogation of prisoners of war. Naval POWs were interrogated by OP-16-Z, the Special Intelligence Section of the Office of Naval Intelligence, which was also responsible for foreign material exploitation (FME). OP-16-Z interrogated prisoners from no fewer than 43 U-boats before the capture of U-505.126 Internal drawings of various types of U-boats derived from some of these interrogations were distributed to the boarding parties of Dan Gallery’s Task Group 22.3 before the cruise ending in the capture of U-505.127

  OP-16-Z also blended HUMINT with FME after USS Roper’s (DD-147) sinking of Eberhard Greger’s U-85 north of Cape Hatteras on April 14, 1942. No one survived the sinking (those who managed to exit the boat were killed in the water by additional depth charges), but an engine room petty officer’s notebook was recovered. This notebook provided OP-16-Z with details on the submarine’s construction, the layout of its engineering spaces, and its operations, all of which was used during subsequent interrogations to obtain more details from captured U-boat crewmen.128

  On June 12, 1943, aircraft from USS Bogue sank U-118, a 1, 600-ton Type XB minelayer under the command of Werner Czygan, west of the Canary Islands. Sixteen survivors were plucked from the water and interrogated. By the middle of July OP-16-Z interrogators had obtained scale drawings of the submarine, as well as technical information on the mines and how they were used. Interrogation techniques had improved, and some prisoners were more willing to divulge information than their counterparts had been earlier in the war. This made it possible for OP-16-Z to obtain information on new enemy technologies that were often still in experimental stages. Interrogators acquired information and drawings on new types of German torpedoes, data on radar detection equipment and methods, modification of armament, and operating tactics.129

  Allied operational and technical personnel considered much of the information derived from POW interrogations to be of immediate importance for modifying ASW equipment and tactics to improve their performance against the U-boats.130

  Tracking U-505’s Position

  F-21, the group Commander Knowles established to track U-boats in the Atlantic Ocean, appears to have taken no notice of U-505’s final departure from Brest until the boat’s commander, Harald Lange, sent his first position report on March 25. Lange reported his position to BdU at 3:34 a.m. on March 25, as “CG 17.”131 This message told his superiors U-505 was leaving the Bay of Biscay. It may or may not have been useful to BdU, but F-21 and the Allied HF/DF network made use of the information. The direction finders obtained a fix on Lange’s signal, placing U-505 at 44-39N 14-30W, or 290 miles from its actual location when Lange sent the message.132 The codebreakers read CG 17 as 40-39N 14-30W, 45 miles from the center of grid square CG 17.133

  Just before midnight on March 28 Lange received orders from BdU.134 These orders were countermanded the next day, but Lange’s radio operators never received the second message canceling the new orders.135 Lange waited until April 1 before sending a position report using the Short Signal codebook.136 The message was garbled, but HF/DF placed the transmitter at 34-00N 18-00W—a difference of 110 miles from the KTB position of 33-57N 20-12W. OP-20-G assessed the contents of the message and determined if the radio operator had intended to send the code group “OKQD” instead of “OKXD,” (the Morse Code for Q is dah-dah-di-dah while X is the closely related dah-di-di-dah), a position of 34-03N 19-42W would be obtained. This point was only 26 miles from U-505’s logged position.137

  U-505 ran southeast on the surface in darkness, submerging in daylight. On April 4 Lange received orders to rendezvous with U-123 the next day to deliver new Enigma keys (code books).138 Early the next morning, he sent a message reporting he was on schedule, only to be informed an hour later the rendezvous had been cancelled.139 Shortly after noon Lange received new instructions and the two U-boats effected their rendezvous on April 7. Oberleutnant zur See Paul Meyer, the boat’s First Watch Officer, carried the new keys to U-123 in a rubber boat.140

  Lange continued south and on April 10 again reported his position, this time in square DS 63.141 He requested orders in the same message, which he received a few hours later. No DF fix was obtained, but the position report was decrypted as 23-33N, 28-27W. The position shown in the KTB, DS 6353, was only 23 nautical miles from the decrypted estimate.142 Lange received his final operating orders—to patrol west of U-190, between 3-42W and 14-30W.143

  Knowles and his staff paid little attention to U-505 as it traveled to its operating area. Any mention of U-505 on the daily location lists for March 26 through April 14, 1944, is limited to brief summaries of the decrypted message traffic and the HF/DF fixes discussed above.144 No effort appears to have been made to predict U-505’s actions, although it should be noted Lange was receiving orders and sending position reports frequently enough that no predictive analysis was necessary.

  Lange’s superiors in BdU kept a daily position estimate for all U-boats at sea. Each position estimate was listed in the same grid square system that U-boat captains used to log and report positions, although the BdU estimate was given to a lesser degree of precision than the reports in the KTB. For example, BdU’s position estimate for March 19 was “BF 41” when Lange logged his position as “BF 7333.” Even so, at that time U-505 was no closer than 138 miles to any point in square BF 41.145 Other position estimates vary similarly, with BdU typically overestimating U-505’s progress, sometimes by more than 400 miles, until receiving the next position report from Lange.

  Lange sent a situation report during the night of May 19. T
he report described the lack of traffic or patrols off Freetown, told of his attempt to catch a British steamer, and announced his intention to head for home on May 21.146 BdU was unable to copy U-505 clearly because of interference, but Allied HF/DF intercepted the message—the first such traffic from U-505 in weeks. The HF/DF network fixed U-505’s position at 3-00N 6-00W, 118 nautical miles from the KTB position of 4-51N 5-21W.147 BdU’s position estimate for U-505 placed it in square EU 80, which at its closest point lay 164 miles from the submarine.148

  Renewed Interest in U-505

  F-211’s U-Boat Intelligence Summary for April 28, 1944, warned of U-505, U-190, and U-155 patrolling “close to the coast in the Gulf of Guinea,” citing BdU’s message 1253/13/340 as its source.149 At this time Knowles was not yet making a daily estimate of U-505’s position on the F-21 submarine plot, and the submarine does not appear in the next summary dated May 13.150 F-21 began paying closer attention to U-505 after intercepting Lange’s May 14 situation report. Knowles included a summary of Lange’s message on the May 15, 1944, location list and included the HF/DF fix for the boat.151 In addition to position estimates for other U-boats in the Atlantic and Mediterranean, F-21’s daily message to the operating forces contained this notice: “DFs over past several days suggest that three U-boats estimated patrolling off African Coast are now homebound from Cape Palmas area.”152 The May 16 location list repeated the DF position, adding, “Will return 21 May.”153 The lists for May 17 through 20 all contained the legend, “Cape Palmas returning 21 May.”154 F-21 began estimating U-505’s noon position on May 21, assessing the submarine’s location as 2-00N 10-00W. Knowles was off by 267 miles from U-505’s actual position, 5-57N 12-03W. However, this figure compared favorably with BdU’s own estimate of square ET 12 (closest point 9-36N 18-36N), an error of 452 miles.155