 During World War II Gleason was part of OP @-@ 20 @-@ G , the U.S. Navy 's signals intelligence and cryptanalysis group , one task of which ( in collaboration with British cryptographers at Bletchley Park such as Alan Turing ) was to penetrate German Enigma machine communications networks . The British had great success with two of these networks , but the third , used for German @-@ Japanese naval coordination , remained unbroken because of a faulty assumption that it employed a simplified version of Enigma . After OP @-@ 20 @-@ G 's Marshall Hall observed that certain metadata in Berlin @-@ to @-@ Tokyo transmissions used letter sets disjoint from those used in Tokyo @-@ to @-@ Berlin metadata , Gleason hypothesized that the corresponding unencrypted letters sets were A @-@ M ( in one direction ) and N @-@ Z ( in the other ) , then devised novel statistical tests by which he confirmed this hypothesis . The result was routine decryption of this third network by 1944 . ( This work also involved deeper math ­ e ­ mat ­ ics related to permutation groups and the graph isomorphism problem . ) 
