TheCodeBreakers
of Norway almost by default. The Germans continued to listen in to
Admiralty messages during the critical summer of 1940 as Hitler
prepared for Operation SEALION—his invasion of England. The crypt-
analytic intelligence had long been entering into operational planning,
and the Oberkommando der Kriegsmarine had come to depend on it.
Suddenly, on August 20, as all England was bracing itself in its finest
hour, and the sky above was streaked with contrails as the few earned
their tribute from the many, the Admiralty, which had finally tumbled to
the German cryptanalysis, changed its codes and ciphers. O.K.M. went
deaf. The abrupt cutting off of quantities of information about British
plans and disposi-
tions caused, a German said, "a great setback for German naval
strategy." No longer could German vessels strike out at the greater
British forces with foreknowledge or move deftly out of their way. British
annaabi.ee 
