Page:Red and Purple - A Story Retold.pdf/3

 RED AND PURPLE

occurrence of two vowels next to each other; the second table shows the alternating vowels.

ADJACENT VOWELS (V-V)

ALTERNATING VOWELS (V-C-V)

The chart of alternating vowels was studied first. The first step in chaining is to look for the highest number in the matrix. This number is 36, which corresponds to position I-O. For the next letter, look in the O row. O-A is the largest occurrence with 35, so the chain I-O-A appears hopeful for a rotor solution. In the A row, the highest frequency is A-I and next is A-Y. The description of the original analysis is hazy at this point, but the end result was that the analysts postulated two separate chains, I-O-A and E-Y-U. From the chart of adjacent vowels, a sequence of Y-O-U-A-E-I made sense, which fit together with (and was perhaps the reason for) the hypothesis from the V-C-V chart. Once the analysts had a sequence for a 6-long wheel, they found it possible to substitute values for vowels in the message, and then to guess plain text, based on their knowledge of past messages.

Next they considered the messages in their ten-day period from December 1936. They isolated sixes and figured out that the order was BEIHOX. However, in the messages they were working, inconsistencies kept appearing. It was finally discovered that some messages had the sequence B-E-I-H-O-X, and others had the sequence X-O-H-I-E-B.

At this point the Navy analysts were consulted to find out if they had worked any similar systems. Lieutenant Wenger of the Code and Signal Section reported that the Navy had worked a machine with a 6-wheel, a 20-wheel, and a break wheel of 47 teeth, some of which were inoperative. 5


 * 4 Ibid., p. 3.
 * 5 Ibid., p. 8.