The only reference I can find regarding this codebook is on page 196 of Ralph Bennett's 'Behind the Battle' (Sinclair-Stevenson, London, 1994): ' . . . but when on 10 June [1943] the Admiralty at last replaced Naval Cipher No. 3 with No. 5, which proved quite secure, it was plain that the U-boats could never regain their former authority.'
This is the front cover of the codebook:
Next is the title page: (Note the date)
The contents page:
No clue given as to the recyphering techniques involved:
From the instructions, we can see that the original book has been subjected to an update which involves some simplifications such as ignoring the 5-letter groups:
Three of the 4 spelling tables have been omitted. Note that the numbers used for spelling overlap other groups and so the group that precedes a spelt word also defines the number of letters.
Worked example: (Note only repeated goup is 'Marseilles')
More groups to assist with interpreting multiple options:
Start of the codebook proper: (note the homophones and general usage of the language)
The first page of dates:
The next set of pages show the numbering system:
Spelling groups:
Note the diphthong and the D' ('S is also defined as a 2-letter pair):
The second half is titled 'Decypher No. 5':
A table for translating spellings concludes the book:
Comments welcome:
klockstone@cix.co.uk