RAF Service numbers are fascinating, as Haraka pointed out there was an algorithm for deducing which letter was allocated as a prefix to the seven numbers.
Step one
Multiply the first number by 8
“ the second by 17
“ the third by 4
“ the fourth by 16
“ the fifth by 2
“ the sixth by 13
“ the seventh by 1
Add them to get ‘Answer A’.
Step two
Divide Answer A by 23 and reduce the number to the nearest integer to ger Answer B.
Step three
Take away Answer B from Answer A,
the result is then applied to the alphabet.
0 = A, 1 = B, 2 = C, 3 = D, etc until 23 = X.
There was a code in the first two digits which defined, Airman (Ground), Airman (Aircrew), Officer (Direct) and Officer (from the ranks). There may have been other codes, but if so, I’ve forgotten them.
My dad was a National Serviceman on entry 109 his number was 2349032 (1947 – 1949)
Mine was in the 8102*** group September 1972.