Harry Bennett provides a detailed report of David McMullan's findings...



1. How the code works

The coded letters are immediately identifiable by the form of the date: 22/3/42 rather than 22 March 1942 indicates it is coded. Underlining the signature also confirms that the letter carries a coded message.



The length of the message is determined by multiplying together the number of letters in the first two words of the first line of the letter after the salutation. Using the letter on which I had based all my attempts (22/3/42) the first 2 words are ‘lucky again’ which is 5 x 5 = 25.



A grid is drawn with 25 squares in it i.e.5 x 5. The rest of the first line is ignored. Starting with the second line of the letter, select the fifth and fourth words alternately and place them in the grid starting top left and working left to right.



However, the message is eventually read starting bottom right, reading across and then diagonally, across and diagonally, etc, as shown below, reading in sequence 1 – 25



25

24

22

19

15

23

21

18

14

10

20

17

13

9

6

16

12

8

5

3

11

7

4

2







If the word ‘but’ occurs as the 5th or 4th letter, it signifies the end of the message. Words which are hyphenated or have an apostrophe in them are treated as one word for the purposes of counting e.g. ‘two-days’, ‘I’ve’.



2. Letter dated 22/3/42

In the 22/3/42 letter, the 5th word is ‘acknowledge’ so this goes into the top left box of the grid and is, therefore, the final word of the message.



The 4th word after this is ‘the’ which indicates that the alphabet code starts at this point. This means that, starting with the next sentence, the first letter of each consecutive word is written down in groups of three, each letter is identified on the alphabet listing shown below and then the number of the column in which it occurs.



Thus, on the 22/3/42 example, you go to the sentence which starts ‘Which brings the’ and list the first letter of every word in groups of three.



Each group of 3 letters signifies a letter in the table. When I originally did this, I used the table starting with O and it produced goobledygook. What David McMullan did was to realise that, if there were variations in the numerical code such as 5 6 and 5 4, then there could well be variations in the alphabet code.

Instead of the O table shown below, the start letter might be different. He worked systematically through the alphabet, looking for the code to produce a word that made sense.



It was not until he got to the 19th letter (S) that he got a recognisable result. The word was ‘elder’ followed by a full stop.



O 111 P 211 Q 311

R 112 S 212 T 312

U 113 V 213 W 313

X 121 Y 221 Z 321

. 122 A 222 B 322

C 123 D 223 E 323

F 131 G 231 H 331

I 132 J 232 K 332

L 133 M 233 N 333



S 111 T 211 U 311

V 112 W 212 X 312

Y 113 Z 213 . 313

A 121 B 221 C 321

D 122 E 222 F 322

G 123 H 223 I 323

J 131 K 231 L 331

M 132 N 232 O 332

P 133 Q 233 R 333



So instead of the O table, we have the S table, shown above, and using the same dated letter, we have the first recognisable word:-

WBT 222 = E

COM 331 = L

PWW 122 = D

HBW 222 = E

OUC 333 = R

ISC 313 = .



We know from John Pryor’s memoirs that his colleague in captivity was Lt.Cdr. Elder. So the 2nd word on the grid and the penultimate word of the coded message is ‘Elder’.



3. Testing the hypothesis

David then chose a letter at random and tried the same approach using the S table.



The letter he chose is dated 7/5/42 and has an underlined signature, both aspects indicating that the letter contained a coded message. The first 2 words of the letter are ‘Last week’ which indicates a grid of 4 x 4 and a coded message of 16 words.



Using the 5 4 S approach, starting with the second sentence, the 5th word is ‘marks’ which becomes the first word in the grid and the last word of the message.



The 4th word is ‘the’ which indicates that the alphabet code starts. Starting with the next sentence, the first letter of each word is listed in groups of 3, converted into numbers on the S table and then into alphabet letters.



ICI 333 R

WHN 222 E

NOT 232 N

EMM 211 T

HHB 222 E

TOT 232 N

RDO 313 .



The word spells ‘renten’ and becomes the second word on the grid. (Don’t worry, he too did not initially recognise this as a ‘real’ word until he googled it and discovered that the currency of Germany from WWI through to 1948 was the renten mark).



At the point where the full stop occurs, you need to revert to the 5 4 sequence at the start of the next sentence in the letter but maintaining the correct rhythm.



Having finished on the 4th word at the previous stage, you start this time again with the 5th word. This gives the word ‘information’ which becomes the 3rd word on the grid.



The following 4th word is ‘especially’ which becomes the 4th word on the grid. The 5th word is ‘and’ which becomes the 5th word on the grid. The 4th word is ‘the’ signalling that the alphabet code starts again at the beginning of the next sentence. This produces the following:-



ARO 133 P

PBM 121 A

PDS 111 S

MFI 133 P

LOE 332 O

IOC 333 R

HAS 211 T

IAU 313 .



It contains a spelling error but is nonetheless recognisable as the word ‘passport’ which becomes the 6th word on the grid.



Reverting to the start of the next complete sentence in the letter and picking up the 5 4 rhythm, the 5th word is ‘borders’ which becomes the 7th word on the grid. The following 4th word is ‘require’ which becomes the 8th word on the grid. The following 5th word in the letter is ‘the’ which indicates that the alphabet code starts again, as follows:-



PAM 111 S

TMN 212 W

ITL 323 I

SMP 111 S

GAA 111 S

FSO 313 .



The 9th word on the grid is ‘swiss’.



Reverting to the start of the next complete sentence in the letter and keeping the 5 4 rhythm, the 4th word is ‘of’ which becomes the 10th word on the grid. The following 5th word is ‘obtained’ which becomes the 11th word on the grid. The following 4th word is ‘local’ which becomes the 12th word on the grid. The following 5th word is ‘some’ which becomes the 13th word on the grid. The following 4th word is ‘the’ which indicates that the alphabet code starts again at the beginning of the next sentence. This produces the following:-



AFW 132 M

AWA 121 A

ARU 133 P

SSM 111 S

CGL 313 .



The 14th word on the grid is ‘maps’.

Reverting to the start of the next complete sentence in the letter and keeping the 5 4 rhythm,

the 5th word is ‘and’ which becomes the 15th word on the grid. The following 4th word is

‘clothing’ which becomes the 16th and final word on the grill. To re-enforce the point, the

5th word after this point is ‘but’ which confirms the end of the coded message. The grid

reads as follows:-



marks renten information especially

and pasport borders require

swiss of obtained local

some maps and clothing



4. Conclusion

Starting in the bottom right corner and reading across and diagonally in sequence, the message reads ‘clothing and local maps obtained require some of borders especially swiss passport information and renten marks’.

