TheCodeBreakers
right down to pencil-and-paper work by individual cryptanalysts.
Such was the solution of the superencipherment of the Japanese TSU
diplomatic code—the columnar transposition with blank spaces in the
transposition blocks that American cryptanalysts called the K9
transposition to the j!9 code. The Japanese embassy in the Soviet Union
began relying heavily on this code in October of 1941, when the Soviet
government moved its capital eastward from threatened Moscow to
Kuibyshev. The diplomats had to stay close to the seat of government,
and the Japanese may have junked their heavy cipher machine instead
of moving it, using their paper codes instead. Pers z made its first break
by spotting two messages which had patches of identical letters
separated by nonidentical sections. Deducing that these differing
portions represented the same placode text, the cryptanalysts compared
the two messages until, in a single afternoon, they found a transposition
annaabi.ee 
