TheCodeBreakers
extended it to four. Instead of punching out holes corresponding to the
most frequent groups, however, Referat IVb marked them with small
crosshatched disks, and looked, not for the brightest spot, but for the
darkest. Stein's mathematicians extensively investigated the question of
how a codegroup stock could be constructed so that this method would
not work against it. Referat IVc's chief was Professor Dr. Wolfgang Franz,
and Ministerial Counselor Dr. Victor Wendland was head of Gruppe V
(Practical Cryptanalysis) and so Fenner's immediate subordinate.
Early in the war, the O.K.W. cryptanalysts worked in a former town
house on one of the streets that run off the Tirpitzufer, not far from
O.K.W. headquarters on the Bendlerstrasse. About 1943 they moved to
much larger quarters in a modern semicircular concrete office building at
56 Potsdamerstrasse called the Haus des Fremden-verkehr—a name that
annaabi.ee 
