Case 6-b.
Message
Lt. J. B. Smith, Royal Flying Corps, Calais, France.
| DACFT | RRBHA | MOOUE | AENOI | ZTIET |
| ASMOS | EOHIE | YOCKF | NOHOE | NOUTH |
| OMEAH | NILGO | OSAHU | OHOUE | APCHS |
| TLNDA | CFTEN | INTWN | BAFOH | GROHT |
| AEIOH | ABRIS | ODACF | TRREN | OSTSM |
| AYBIS | DFTEN | EFAPH | OSMNI | ZTIEA |
| HLILL | TWSOU | GDENO | UTHOM | EAHBH |
| AMOOU | EAYOE | QISUU | OLEHA | DENOE |
| NHOOQ | OBBOR | TSLHO | BAHEO | UBHOB |
| IHTSW | ENOHO | PAHIH | ITUAS | BIHTL |
Graham-White.
The address and signature indicate that this message is in English.
There are 250 letters in the cipher; the vowels AEIOU occur 109 times or 43.6%, the letters LNRST occur 62 times or 24.8%, and the letters KQVXZ occur 5 times or 2%. The proportion in the case of the vowels is somewhat too large and, in the case of the letters LRNST, it is too small. It is then questionable whether this is a transposition cipher altho, at first glance it might appear to be one.
On examination for parts of possible words we are at once struck by the occurrence at irregular intervals of recurring groups, viz:
| DACFTRR | ENO | BHAMOOUEA |
| DACFTEN | ENOUTHOMEAH | BHAMOOUEA |
| ENO | ||
| DACFTRR | DENOUTHOMEAH | IZTIE |
| FTEN | DENO | IZTIE |
| ENO |
This is a strong indication that the cipher is a substitution cipher, so, to make an examination a frequency table will be constructed.