I am getting really bloody confused about this thread now
To help you understand:
Two Ronnies - F.U.N.E.X?BTW
Siam = Sexual Intercourse After Midnight
Norwich = Knickers Off Ready When I Come Home
Burma = Be Undressed Ready My Angel
All used by servicemen on the envelopes of letters to their sweethearts as a way of getting a message of their likely opportunity for leave which the censors would have taken out of their letters.