“There is… only one fully trained individual among the permanent force”: Johnson, Neglected Giant, 20.
On June 1, 1939, the Japanese fleet began using: Descriptions of how JN-25 worked are in RG 38, Box 116, “CNSG-OP-20-GYP History for WWII Era (3 of 3)” and “CNSG History of OP-20-GYP-1 WWII (1 of 2).”
“First break [was] made by Mrs. Driscoll. Solution progressing satisfactorily”: RG 38, Box 115, “CNSG OP-20-GY History.” Also Kahn, “Pearl Harbor and the Inadequacy of Cryptanalysis.”
Years after World War II ended: “I saw not all that long ago maybe eight or ten years ago, two people who had served in FRUPAC and one in Washington, who were still arguing about the value of a code group.” Captain Prescott Currier, oral history interview on April 14, 1972, NSA-OH-02-72, 32.
“In the navy she was without peer as a cryptanalyst”: Layton et al., And I Was There, 58.
“If the Japanese Navy had changed the codebook along with the cipher keys”: RG 0457, 9002 (A1), Box 36, SRH 149, “A Brief History of Communications Intelligence in the United States” by Laurance F. Safford, 15.
Chapter Three: The Most Difficult Problem
On an upper floor, occupying: David Kahn, “Pearl Harbor and the Inadequacy of Cryptanalysis,” Cryptologia 15, no. 4 (1991): 282, DOI: 10.1080/0161-119191865948.
Sometimes in private they called him “Uncle Willie”: RG 0457, 9002 (A1), Box 17, SRH 58, “The Legendary William F. Friedman.”
As the staff expanded, Friedman had done something else: RG 0457, 9032, Box 751, “SIS Organization and Duties/SIS Personnel,” and Box 779, “Signal Intelligence Service (SIS) General Correspondence Files.”
The Coast Guard’s mission was enforcing “neutrality”: R. Louis Benson Interview of Mrs. E. S. Friedman, January 9, 1976, Washington, D.C., https://www.nsa.gov/news-features/declassified-documents/oral-history-interviews/assets/files/nsa-OH-1976-22-efriedman.pdf.
In October 1939, following the outbreak of war in Europe: RG 0457, 9002 (A1), SRH 361, “History of the Signal Security Agency,” vol. 1, “Organization,” part 1, “1939–45.” NSA Cryptologic Histories, https://www.nsa.gov/news-features/declassified-documents/cryptologic-histories/assets/files/history_of_the_signal_security_agency_vol_1SRH364.pdf.
Berryman hailed from Beech Bottom, West Virginia: Wilma Berryman Davis, oral history interview on December 3, 1982, NSA-OH-25-82, 2–8.
Asking around, Wilma Berryman found out: A history of the naval correspondence course is in Chris Christensen and David Agard, “William Dean Wray (1910–1962)the Evolution of a Cryptanalyst,” Cryptologia 35, no. 1 (2010): 73–96, DOI: 10.1080/01611194.2010.485410.
It was a teach-yourself kind of place: Frank Rowlett, oral history interview in 1976 (otherwise undated), NSA-OH-1976-(1-10), 380.
“What four things were thought by Captain Hitt to be essential”: RG 0457, 9032, Box 751, “Army Extension Course in Military Cryptanalysis.”
Since the United States was not, strictly speaking, at war: Rowlett in his oral history NSA-OH-1976-(1-10), 350, says, “We knew it was illegal” but “we figured that as long as we didn’t let it be openly published that we were still legal if we intercepted and if we cryptanalyzed… that we sort of had a little bit of an island to stand on.”
The Communications Act of 1934: RG 0457, 9032 (A1), Box 1019, “Notes on History of Signal Intelligence Service,” 76.
And there was twenty-seven-year-old Genevieve Marie Grotjan: RG 0457, 9032, Box 780, “Signal Intelligence Service—General Correspondence file 1941”; Genevieve Grotjan, interview with David Kahn, May 12, 1991, National Cryptologic Museum Library, Fort Meade, MD, David Kahn Collection, DK 35–44, notes; Personnel Record Folder for War Department Civilian Employee (201) file: “Grotjan, G.,” National Personnel Records Center, National Archives, St. Louis, MO.
She was known for her thoroughness, powers of observation: Frank B. Rowlett, The Story of Magic: Memoirs of an American Cryptologic Pioneer (Laguna Hills, CA: Aegean Park Press, 1998), 128.
Friedman’s office kept its own “nut file,” recording the outlandish systems: Abraham Sinkov, oral history interviews, NSA-OH-02-79 through NSA-OH-04-79.
The first message in the new machine cipher: RG 0457, 9002 (A1), SRH 361, “History of the Signal Security Agency,” vol. 2, “The General Cryptanalytic Problems,” 31–32. Also available online from NSA “Cryptologic Histories.”
The British had tried to break: RG 0457, 9002 (A1), Box 92, SRH 349, “The Achievements of the Signal Security Agency in World War II,” 17.
The U.S. Navy, in the wing next door, worked on Purple: Frank Rowlett, oral history interview on June 26, 1974, NSA-OH-01-74 to NSA-OH-12-74, available in notebooks (not online) at National Cryptologic Museum Library, 457.
Friedman’s team had figured out that the old Red: Kahn, “Pearl Harbor and the Inadequacy of Cryptanalysis,” 280–281; “History of the Signal Security Agency,” vol. 2, 32; William Friedman, “Preliminary Historical Report on the Solution of the ‘B’ Machine,” October 14, 1940, https://www.nsa.gov/news-features/declassified-documents/friedman-documents/assets/files/reports-research/FOLDER_211/41760789079992.pdf; Rowlett, Story of Magic, 145.
Frank Rowlett liked to go to bed early: Kahn, “Pearl Harbor and the Inadequacy of Cryptanalysis,” 282.
William Friedman often thought of solutions: Davis, oral history, 13.
He studied how French letters behaved: RG 0457, 9032 (A1), Box 751, “Army Extension Course in Military Cryptanalysis.”
They had mastered the behavior of romanized Japanese: Rowlett, Story of Magic, 117.
They reviewed the workings of known machines: Ibid., 138.
When the Purple machine was being installed in Japanese embassies: Ibid., 139.
The code breakers talked to radio intercept operators: Ibid., 141.
Friedman liked his team to do their own pen work: Grotjan interview with Kahn.
Cribs are educated guesses about what: Kahn, “Why Weren’t We Warned?” 56. Stephen Budiansky, Battle of Wits: The Complete Story of Codebreaking in World War II (New York: Free Press, 2000) also describes the importance of cribs.
The fact that they had broken the sixes meant: “History of the Signal Security Agency,” vol. 2, 33–34.
They theorized that the Purple machine was using some kind of switching device: Rowlett, Story of Magic, 150.
Their hopes renewed by this latest theory, Frank Rowlett and his Purple team: “History of the Signal Security Agency,” vol. 2, 41.
Mary Louise Prather—keeping her meticulous files: RG 0457, 9002 (A1), Box 37, SRH 159, William F. Friedman, “The Solution of the Japanese Purple Machine.”
“We were looking for this phenomenon,” he would later say: Frank Rowlett, oral history, NSA-OH-01-74 to NSA-OH-12-74, 283.
Sitting there engrossed in what Rowlett later rather sheepishly: Ibid.
She was “obviously excited”: Rowlett, Story of Magic, 151.
Then, at the end of a long stream of letters, she circled a third: Some accounts have her circling three spots, but Rowlett, Story of Magic, 152, says four.