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X-WR-CALDESC:5 March 1942: Station HYPO started reading Japanese JN-25. Pho
 to is of Captain Joseph Rochefort.\n\nCommander Joseph Rochefort had been 
 placed in command of Station Hypo\, the Navy's codebreaking organization a
 t Pearl Harbor. In 1942 Rochefort and his staff began to slowly make progr
 ess against JN-25\, the Japanese Navy's operational code. If it could be b
 roken\, Rochefort would be able to provide Nimitz the information he neede
 d to make wise and prudent decisions concerning the dispersal of his preci
 ous naval assets.\n\nBreaking the Japanese code known to Americans as JN-2
 5 was daunting. It consisted of approximately 45\,000 five-digit numbers\,
  each number representing a word or phrase. For transmission\, the five-di
 git numbers were super-enciphered using an additive table. Breaking the co
 de meant using mathematical analysis to strip off the additive\, then anal
 yzing usage patterns over time\, determining the meaning of the five-digit
  numbers. This complex process presented a challenge to the officers and m
 en of Station Hypo\, but Rochefort and his staff were able to make progres
 s because the system called for the repetitive use of the additive tables.
  This increased the code's vulnerability. Even so\, the work was painfully
  slow. Prior to the attack on Pearl Harbor\, only 10% to 15% of the code w
 as being read. By June of 1942\, however\, Rochefort's staff was able to m
 ake educated guesses regarding the Japanese Navy's crucial next move.
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X-WR-TIMEZONE:America/New_York
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TZID:America/New_York
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TZNAME:EST
DTSTART:20251102T020000
TZOFFSETFROM:-0400
TZOFFSETTO:-0500
RDATE:20261101T020000
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TZNAME:EDT
DTSTART:20250309T020000
TZOFFSETFROM:-0500
TZOFFSETTO:-0400
RDATE:20260308T020000
RDATE:20270314T020000
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BEGIN:VEVENT
UID:3cc5ed2f-f0fa-4d4e-9351-f904bdff0d1c
DTSTAMP:20260424T064516Z
DESCRIPTION:5 March 1942: Station HYPO started reading Japanese JN-25. Phot
 o is of Captain Joseph Rochefort.\n\nCommander Joseph Rochefort had been p
 laced in command of Station Hypo\, the Navy's codebreaking organization at
  Pearl Harbor. In 1942 Rochefort and his staff began to slowly make progre
 ss against JN-25\, the Japanese Navy's operational code. If it could be br
 oken\, Rochefort would be able to provide Nimitz the information he needed
  to make wise and prudent decisions concerning the dispersal of his precio
 us naval assets.\n\nBreaking the Japanese code known to Americans as JN-25
  was daunting. It consisted of approximately 45\,000 five-digit numbers\, 
 each number representing a word or phrase. For transmission\, the five-dig
 it numbers were super-enciphered using an additive table. Breaking the cod
 e meant using mathematical analysis to strip off the additive\, then analy
 zing usage patterns over time\, determining the meaning of the five-digit 
 numbers. This complex process presented a challenge to the officers and me
 n of Station Hypo\, but Rochefort and his staff were able to make progress
  because the system called for the repetitive use of the additive tables. 
 This increased the code's vulnerability. Even so\, the work was painfully 
 slow. Prior to the attack on Pearl Harbor\, only 10% to 15% of the code wa
 s being read. By June of 1942\, however\, Rochefort's staff was able to ma
 ke educated guesses regarding the Japanese Navy's crucial next move.
DTSTART;TZID=America/New_York:20260305T000000
DTEND;TZID=America/New_York:20260305T235900
LOCATION:
SUMMARY:1942: Station HYPO began reading Japanese system JN-25.
END:VEVENT
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