I I I ARAE_RE_ _ ENT O O O Now Z is always prefixed by S and may be L. Taking X=I and D=O, (they are certainly vowels), V=G and Y=M, we have ARA EL REGIMIENTO Substituting these values in the rest of the message we have Q DBYPBXH YSOXPCP YSHCSED RBSZPTPB _ ORMARIN ME_IATA MENTE_O _RELA_AR BSCSB PSHSZ AJHCD OSEXVHPODA RETER AENEL __NTO _E_IGNA_O_ We may now take Q=F, O=D, E=S, R=B, T=C, A=P and J=U and the message is complete. We are assisted in our last assumption by noting that S=E and E=S, etc., and we may on that basis reconstruct the entire alphabet. The letters in parenthesis do not occur in the message but may be safely assumed to be correct. Ordinary A B C D E F G H I J L M N O P Q R S T U V X Y Z Cipher P R T O S (Q) (V) N (X) (U) (Z) (Y) (H) D A F B E C J G I M L It is always well to attempt the reconstruction of the entire alphabet for use in case any more cipher messages written in it are received.---- 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. Frequency Table