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1929 - Henry Stimson closed America's Black Chamber unit led by Herbert Yardley, and transferred code operations to the secret Signal Intelligence Service led by William Friedman in the Army Signal Corps. The Navy had established a "research desk" in Room 1621 of the old Navy building under Lt. Laurence F. Safford with civilian cryptographer Agnes Meyer Driscoll who used IBM Hollerith card sorting machines to break the Japanese Red Book code. By 1939, this became OP-20 G within the Code and Signal Section of ONI.
1937 - Signal Corps officer Joseph Mauborgne used a Dictaphone to record Japanese radio signals at the San Francisco Presidio.
1939 - In August, the British moved codebreaking operations to Bletchley Park 40 miles northwest of London between Cambridge and Oxford, later renamed Government Code and Cypher School (GC&CS also referred to as the "Golf, Cheese and Chess Society") commanded by Alastair Denniston, including geniuses such as Ian Fleming, later author of the James Bond novels, and Alan Turing who developed a theory of the electronic computer. (Momsen)
Feb 12, 1940 - The British minesweeper HMS Gleaner depth charged and forced the U-33 to the surface, allowing the capture of rotors used in the German Engima machines. The British continued to capture code information from German weather ships seized in 1940. On May 9, 1941, the British destroyer Bulldog captured the German U-110 commanded by Fritz-Julius Lemp who had sunk the Athenia in 1939, and with it seized a complete Engima machine with its rotors and charts. The capture of the U-110 was one inspiration for the Universal film U-571
June 12, 1940 - British decoded a Luftwaffe message that became the first success of Ultra. It described a German radio beam to guide Luftwaffe to the Rolls-Royce factory in Derby that made RAF engines, and the beam was jammed.
August 30, 1940 - the B-Dienst intercepted and solved a report that convoy SC 2, coming out of Sydney, Canada, would be at 50° 00' north latitude, 19° 50' west longitude, at noon on 6 September. U-boats sank five of the ships and Donitz praised the B-Dienst as a "major help" in the operation. On November 11, 1940, the Germans captured the British ship Automedon, from which they obtained the British merchant ship codes, improving the information B-Dienst provided to the U-boats. In 1943 the B-Dienst intercepted 3,101,831 messages and processed many of them on its 6 Hollerith tabulators. These helped the B-Dienst to solve intercepts in time for the command to use them. Shipping information also was given to the Germans by the Swiss who obtained it from American maritime insurance companies. (Kahn, Momsen)
Sept. 20, 1940 - Genevieve Grotjan completed the decryption of the Japanese Purple code at the Army's SIS, and shared the decoding with the Navy's OP-20-G (Navy on odd days). RCA provided equipment for a room at the Mayflower Hotel for the messages to be photographed and distributed to top government officials.
Nov. 14, 1940 - German Luftwaffe bombed Coventry but it was a myth that Churchill sacrificed the city to save the Ultra secret.
Mar. 25, 1941 - Station X decrypted an Italian Enigma message indicating the italian fleet was going to interdept a British convoy from Egypt to Greece. The British Navy attacked and turned back the Italian fleet.
Sept. 12, 1941 - A Bletchley Park report stated that "the killing of Jews on the Russian Front by the SS provided evidence of 'a policy of savage intimidation, if not ultimate extermination.' The intercepted messages confirm that Churchill knew in the early stages of the war that Hitler had embarked on a campaign of massacring Jews." (Evans)
Dec. 1941 - The Germans intercepted the reports of the U.S. military attache Bonner Fellers in Cairo, and learned of British plans in North Africa. "One fine piece of work did yield extraordinary results. This was the German solution of the American military attache code. Among the attaches who used it was the man in Cairo, Colonel Bonner Fellers, a perceptive and hardworking officer. In late 1941 and early 1942 he reported on the events, the nature, and the course of this new desert warfare." (Kahn)
May 1942 - U.S. Navy codebreakers broke theJN25b code - "'JN' for Japanese Navy, '25' for the 25th code they had worked on, 'b' for its second edition. It had come into use near the end of 1940, and by early 1942 the Americans had recovered enough codegroups to read bits and pieces of Japanese messages." (Kahn)
Aug. 1942 - Ultra helped British stop Rommel in North Africa at Alam Haifa. "For the Eighth Army, the Battle of Alam Haifa was a resounding success. It has been described historically and contemporaneously as the centerpiece of the Allied victory in the desert war, the crucial time when momentum changed sides. The opposing forces were matched as they never would be again. . . .Following the First Alamein, the Eighth Army had taken a line of defense from the sea south to the impassable Qattarra Depression, protecting the Ruweisat and Alam Halfa ridges to the east. Before his supplies dwindled even more, Rommel meant to bring the Eighth Army to a climactic battle for the approaches to Alexandria. His plan depended entirely upon surprise and swift exploitation. After a demonstration in the north, Rommel planned to make his main assault through what he believed was a thinly mined, thinly defended corridor between Ruweisat ridge and the Qattarra Depression. Having breached the British left flank with his armored forces, he would take advantage of the confusion and surprise by sending his Panzers 40 kilometers more before turning them northward to threaten the Eighth Army's line of communications. The British defense was far more spirited and well organized than Rommel expected. Rommel's armor, harrassed by a thick screen of mines and the Seventh Armored Division, was forced to make its left wheel earlier than planned. In the meantime, Montgomery had refused his left flank and anchored his own armor on the western end of the Alam Haifa ridge. The German armor turned unknowingly into these prepared defenses and crashed fiercely against them. After the assault deteriorated along Alam Haifa ridge, the Axis forces disengaged and reasserted their original defense line to the west." (Kahn)
Feb. 1, 1942 - The German Navy added a fourth rotor to the Shark Enigma on Feb. 1, 1942, preventing the Allies from reading messages to German subs until Joe Desch at NCR in Dayton, Ohio, designed a 7-foot-tall, 11-foot-long, 5,000-pound electromechanical bombe to break the 4-rotor code by June 5, 1943. The shift "by the Kriegsmarine to an Enigma using four rotors instead of just three did not halt Bletchley, astonishingly enough, for more than a few days. Eventually, the Allies were able to pinpoint and sink the submarine fuel ships, as well as the attack U-boats themselves, and so with ULTRA'S help were able to win decisively this most decisive of battles." (Kahn)
1942 - Bletchley Park decrypted ciphers of the Abwehr, the German military espionage agency. "The intercepts told the British two important facts: that they had captured all the German spies in their islands, and what the Abwehr thought about its spies. The British deception organization found this information very useful in persuading the Germans, before the D-Day invasion, that the Normandy landing would be a feint." (Kahn)
Feb. 1, 1943 - Army SIS began the Venona program to intercept and decrypt messages between the Soviet goverment and Soviet spies in the Western hemisphere. In Oct., Lt. Richard Hallock made a breakthrough in breaking some of the code. In 1944, Cecil Phillips broke the KGB double-encrypted code. The 2200 Venona messages revealed a large KGB spy ring with code names that would later be identified as Julius and Ethel Rosenberg, scientist Klaus Fuchs (who gave the atomic bomb data to Ruth Werner at Oxford in 1941 that allowed the Russians to begin their A-bomb project in 1943 under physicist Igor Vasilievich Kurchatov), machinist David Greenglass, and especially Harvard scientist Theodore Alvin Hall code-named ''Mlad'' revealed in the 1997 book Bombshell
March 8, 1943 - The German Navy switched to an Enigma with four rotors. "Even a shift on 8 March 1943 by the Kriegsmarine to an Enigma using four rotors instead of just three did not halt Bletchley, astonishingly enough, for more than a few days. Eventually, the Allies were able to pinpoint and sink the submarine fuel ships, as well as the attack U-boats themselves, and so with ULTRA'S help were able to win decisively this most decisive of battles." (Kahn)
April 18, 1943 - "Communications intelligence contributed in two other major ways to the Allies' Pacific victory. It stepped up American submarine sinkings of the Japanese merchant fleet by one third. This cutting of Japan's lifelines was, Premier Hideki Tojo said after the war, one of the major factors that defeated Japan. And, secondly, it made possible in 1943 the dramatic mid-air assassination of Admiral Yamamoto." (Kahn)
July 15, 1943 - Sigsaly digital telephone system between Pentagon and Selfridges Department Store in London, with extensions to Churchill's War Cabinet Rooms and Roosevelt's White House.
Oct. 9, 1943 - The Purple code, broken by William Friedman at SIS in 1940, allowed the U.S. to read the dispatches of Oshima in Germany and learn Hitler's plans. "U.S. army and navy codebreakers, led by William F. Friedman, one of the greatest cryptanalysts of all time, began attacking this top-level Japanese system around the beginning of 1939. In August of 1940, after 20 months of work that in other fields would be worthy of a Nobel Prize, they submitted their first completely solved PURPLE message. The PURPLE solution could not prevent the Pearl Harbor attack. Nor did it help much in the war in the Pacific, where the diplomats had little to do. It made its greatest contribution in the war in Europe. For it enabled the Allies to read the messages ofJapan's ambassador and military attaché in Germany as they reported on Hitler's capabilities and plans. . . . On 9 October 1943 the Allies read a message of a few days earlier in which Baron Hiroshi Oshima, the Japanese ambassador, reported that he had recently visited Hitler in his East Prussia headquarters. Among many other items of interest, Hitler told him that 'I am inclined to believe' that the Allies would land in the Balkans instead of moving north in Italy." (Kahn )
Jan. 1, 1944 - Anthony Blunt was a Soviet spy inside Bletchley Park and told the Russians that the Enigma code was broken, but most of the information provided by this "fourth man" in Britain's Cambridge spy ring led by Kim Philby (with Guy Burgess, Donald Maclean, and the mysterious "fifth man John Cairncross who leaked information about Bletchley Park codebreaking to the Russians, and whose identity was unknown until 1990), including the real plans for D-Day, was not used by the Soviets.
June 1,1944 - Bletchley Park had developed Colossus I by 1943, one of the early electronic computers. Its successor, Colossus II, went into operation on June 1, 1944, confirming that Hitler expected the D-Day invasion at Calais, not Normandy. Another electronic computer, the Harvard Mark I developed by Howard Aiken and IBM in 1944 helped the US Navy to compute mathematical and navigation tables. George Stibitz at Bell Telephone Laboratories developed tracking and aiming devices for anti-aircraft guns by 1944 from his Model-K telephone relay developed in 1937. German engineer Konrad Zuse had developed by 1941 a computer, the Z3, to design airplanes and missiles but it was kept secret and never exploited by the Germans. The pioneering ABC computer developed in 1939 by John V. Atanasoff andJohn Berry at Iowa State University influenced John Mauchly and J. Presper Eckert to start work on the ENIAC in 1943 at the University of Pennsylvania for the U.S. Army's Aberdeen Proving Ground.
Aug. 7, 1944 - The Ultra decryptions helped the Allies break out of the Normandy beachhead and win the battle of the Falais Gap after learning of Hitler's order of Aug. 7 to attack at Mortain. "The Americans had just broken out and were pouring through Avranches. The narrow opening created a target that tempted Hitler. He directed Field Marshal Gunther von Kluge, the commander in chief west, to pull at least four armoured divisions out of the front and hurl them against this bottleneck to close it. Hitler's order was, however, intercepted and solved." (Kahn)
Aug. 25, 1944 - The liberation of Paris was the culmination of the rapid pursuit and destruction of German forces in the Battle of France using knowledge from Ultra. "The completeness and continuity of this information was its chief contribution. In Normandy in 1944, for example, ULTRA was revealing routine daily Luftwaffe reports on the condition of airfields, the number and condition of anti-aircraft guns, the number of planes that could fly, unit strengths. It disclosed the location and movements of specific divisions, the subordination and transfer of units, the boundaries between units - once enabling the U.S. 7th Army to foresee and then to stop cold a German counterattack in Alsace. It gave insights into personnel losses and problems - the death in an air raid of the chief of staff and other officers of Panzer Gruppe West, the weak-kneed response of the commander of the Cherbourg garrison to Hitler's command to hold out like Gneisenau at Kolberg. ULTRA seemed to reveal every single detail of enemy activity. The thousands of bits of information that it provided eased thousands of decisions for Allied commanders and helped them optimize their resources in thousands of cases. Said the U.S. 7th Army intelligence officer after one particularly good morsel arrived: 'You know, this just isn't cricket!" Altogether, ULTRA let the Allies advance into Germany with far more speed than otherwise." (Kahn)
Sept. 12, 1944 - The USS Pampanito carried the Sigaba machine and was able to locate and attack a Japanese convoy out of Singapore. "One form of the American SIGABA (ECM, or 'electric code machine', in its Navy version) used no fewer than ten rotors at a time five to create the electrical maze, five for moving the others in a much more irregular way than gears could. A cryptologist has said that the SIGABA was 'a generation ahead' of the Enigma." (Kahn)
1945 - By the end of the war, the code-breaking organizations in Britain and the U.S. were centralized and tightly coordinated, unlike the dispersed organization in Germany. "The army, the navy, and the air force each had its own unit, though there was rather more justification for that. But this multiplicity spread the available manpower, which was scarce to begin with, very thin. And it diffused the codebreaking effort. Contrast this with the concentration of effort at Bletchley Park, Britain's sole codebreaking agency, and with that in America, where the army and navy codebreaking units worked in the closest co-operation. There was some co-operation in Germany, of course. But it did not overcome the lethal effects of dispersion, which stemmed ultimately from Hitler's assigning duplicate responsibilities to his underlings so that he could retain ultimate control. The charismatic nature of his leadership enabled him to do this in many areas of government. It facilitated his rule - but it devastated his war effort, including codebreaking. . . . The Allies put better men into cryptology than the Germans. Bletchley Park was an unbelievable galaxy of talent. All American recruits were given an IQ test; those who scored the highest were proposed for cryptologic work. This resulted in extraordinarily high brainpower in codebreaking units. The American army agency could have staffed a first-class university in all departments, one of its leaders said. No such recruiting seems to have taken place for German codebreaking. " (Kahn)