A brief study of this table and the distribution in the cipher leads to the conclusion that B, F and C are certainly vowels and are, if the normal frequency holds, equal to E, O, and A or I. Similarly D and I are consonants and we may take them as N and T. I is taken as T because of the combination IP (=possibly TH) occurring three times. The next letter in order of frequency is A; it is certainly a consonant and may be taken as R on the basis of its frequency. Let us now try these assumptions on the first two lines of the message. We have A A A R E N _ O R _ E _ E N T _ _ _ _ _ N T O N _ N _ I I I This is clearly the word REINFORCEMENTS and, using the letters thus found, the rest of the line becomes AMMUNITIONAND. We have then the following letters determined: Arbitrary letters A B C D E F G H I J K L M Plain Text R E I N F O C M T S A U D If these be substituted we have for the message: REINFORCEMENTS AMMUNITION AND RATIONS MUST ARRI_E _EFORE T_E FIFTEENT_ OR _E CANNOT _O_D OUT_. From this the remainder of the letters are determined: Arbitrary letters N O P Q R S Plain text V B H W L X Now let us substitute the two-letter groups for the arbitrary letters: Arbitrary letters K O G M B E P C R H D F A J I L N Q S Two-letter groups GG RG AG NG TG GR AR NR GA RA AA NA RN AN NN TN GT RT AT Plain text A B C D E F H I L M N O R S T U V W X It is evident that the cipher was prepared with the letters of the word GRANT chosen by means of a square of this kind: G R A N T G A B C D E R F G H I K A L M N O P N Q R S T U T V W X Y Z Thus TG=E, AN=S, etc., as we have already found. Case 9-b Message 1950492958 3123252815 4418452815 2048115041 2252115345 5849134124 5028552526 5933195222 5245113215 6215584143 2861361265 2945565015 2342455850 6345542019 1550185311 2115415828 1124174553 4554205950 2552454132 1533492048 5018152364 An examination of the groups of two numerals each which make up this message, shows that we have 11 to 36 and 41 to 65 with eleven groups missing. Now the 11 to 36 combination is a very familiar one in numeral substitution ciphers (See Case 6-c) and it will be noted that 41 to 66 would give us a similar alphabet. Let us make a frequency table in this form: Group Frequency Group Frequency