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 shoulders of the other members of the J-section, thus giving the latter more time for research on the B-machine than would have otherwise been possible. For the original suggestion of the electrical telephone switching mechanism for duplicating the encipherment of the "6's", the design and construction, in collaboration with Mr. Rowlett, assisted by other members of the section, of the machine for deciphering the "6's" and for excellent work in the decipherment of the "6's" in current traffic over many months, Cryptographic Specialist (now 1st Lieutenant) Leo Rosen is to be mentioned. He also supervised and assisted in the construction of the hand-operated B-machine designed by the cryptanalytic staff of the J-section; in this latter project Junior Cryptanalyst H. F. Bearce, Cryptographic Specialist Edward J. Hawkins, Sgts. Wilder end Roy also assisted. In thiis connection, it should also be mentioned that the shop facilities of the Radio Laboratory, Navy Yard, were kindly placed at our disposal and certain materiel furnished thereat, through the courtesy of Commander L.F. Safford of the Communications Security Group, Office of Naval Communications. This greatly facilitated the construction of the hand-operated B-machine. The excellent work of Tabulating Machine Supervisor Ulrich J. Kropfl end Cryptanalytic Aide Mary J. Dunning in performing countless tabulating machine operations deserves mention, as well as the painstaking work of the various card punch operators under their supervision. Miss Dronenburg performed and assisted in many clerical jobs of routine and special nature in connection with these studies. The work of Research Analysts John B. Hurt and Paul S. Cate must be mentioned in connection with our efforts to reconstruct the texts of messages in Japanese. This difficult work had to be done in what little time could be spared from their regular and arduous duties as translators. The work of Cryptographic Clerk Frances M. Jerome in maintaining the files of the intercept traffic necessary to these studies proved to be extremely helpful; her everyday work in operating the "6's" deciphering machine was painstaking and accurate. To Cryptographic Clerk Mary Louise Prather credit should be given for the careful keeping of the records and index of all messages; it was also she who found the paraphrased K-1 message mentioned in Par. 6, and which played an important part in the final break into the system. After the initial solution of the "20's" had been made there was great pressure to hurry the work along as fast as possible. In addition to considerable overtime work by members of the J-section, certain personnel from other sections of the S.I.S. were brought in to assist. Some of them performed this work only as voluntary overtime. In this special assistance the names of the following persons are to be mentioned: Associate Cryptatanalyst Abraham Sinkov, Assistant Cryptanalyst Lawrence Clark, Junior Cryptanalyst Delia Ann Taylor, Cryptographic Clerk Wilma Z. Berryman, and Cryptographic Specialist Edward E. Christopher, Jr.

The vigilance and excellent work done by our various monitor stations in intercepting and copying the necessary traffic also deserves special mention. The assistance rendered by G-2 in obtaining certain data bas already been mentioned.

The undersigned was directed to participate in the "B" machine studies in August 1939, and from that time on these studies were under his general supervision, at the same time that he carried on some of the duties from which he had not been relieved. In addition to this general supervision