M S I B R O R S E E V U E E M C O R E R E L I D E T O E P Q E N R E R N S E R Y E C O L L E R E U S P L U R C E L O A J A E H U H P F A S O N N O A A E P I U A P P E A C U Q A R U O P O E I I R R M I A F D A A R Q U B O Z A E G E R S F S X There are 120 letters in this message with 57 vowels or 47% vowels, and the letters LNRST occur 31 times or 26% of the whole. Non-occurrence of K and W and vowel proportion leads us to the assumption that it is a transposition cipher of a Spanish text. The factors of 120 are 5 × 3 × 2 × 2 × 2. We may then have one rectangle of 4 × 30 or one of 5 × 24 or two of 5 × 12, or three of 5 × 8, or four of 5 × 6, or five of 3 × 8, or ten of 3 × 4, or twenty of 3 × 2. The message being in a rectangle of 4 × 30, we can inspect it as it stands and this is clearly not the arrangement if it be a geometrical transposition cipher at all. It is best however to try the largest possible rectangles first so we will put it in the form 5 × 24, thus: M S I B R O R S E E V U E E M C O R E R E L I D E T O E P Q E N R E R N S E R Y E C O L L E R E U S P L U R C E L O A J A E H U H P F A S O N N O A A E P I U A P P E A C U Q A R U O P O E I I R R M I A F D A A R Q U B O Z A E G E R S F S X Here an inspection shows this to be Case 1-f, alternate diagonal, and the text to be "ME SITUO SOBRE PARRAL PORQUE ME PRESENCIA FUE REVELADA POR U"; here the sense breaks but note that U is the twelfth letter of the line and continue as if the rectangle were 5 × 12 and we have "NA PAREJA QU." Now inspect the second rectangle of 5 × 12 in the same way and the sense continues "E SE ME ACERCO Y HUBO QUE RECHAZAR POR EL FUEGO ALLI ESRERO ORDENES FINISX". The practical way of examining a cipher of this type is to have several men prepare rectangles of different dimensions, using the letters of the cipher in the order received. The rectangles can be inspected very rapidly when once prepared. Note that the dimensions of any rectangle will rarely be such as to contain more than fifty letters, on account of the necessity of filling up a rectangle with nulls if the number of letters of the message is just a little greater than a multiple of the rectangle. Also large rectangles give, for all but the diagonal method, whole words in a line or column and these are easily noted. The following ciphers come under Case 1: Case 1-i.--The rail fence cipher, useful as an operators' cipher but permits of no variation and is therefore read almost as easily as straight text when the method is known. The message: HOSTILE CAVALRY HAS RETIRED is written: O T L C V L Y A R T R D H S I E A A R H S E I E and is sent: OTLCV LYART RDHSI EAARH SEIEX Case 1-j. Message