TheCodeBreakers
system had to be determined, the superencipherment stripped off, and
the repertory then built up. This would have imposed much greater
difficulties than just solving another codebook edition—except for
American alertness.
Forty minutes after midnight, the American intercept post at Souilly
picked up one of the first messages in the new system. Station x2 was
sending it to station AN:
00:25 CHi-13 845 422 373 792 240 245 068 652 781 245 659 504
At 12:52 AN replied: CHI-13 os RGV KZD. Five minutes later x2 sent a
second message to AN:
00:25 CHI-14 UYC REM KUL RHI KWZ RLF RNQ KRD RVJ UOB KUU UQX UFQ RQK
When these appeared on the desk of code cryptanalyst Lieutenant
Hugo Berthold, he guessed at once what had happened: x2 sends a 13-
group cipher message (cHi-13) in a new system. AN responds with os, a
well-known service abbreviation for Ohne Sinn ("message unintelligible"),
and a reference to cm-13, followed by two groups from the old KRU code.
annaabi.ee 
