naval message abbreviations

[drahtlose]

In doing research with naval records for WWI and later, I have found that naval messages are numbered and preceded by an abbreviation. I have collected the following:

C.P.

N.

M.

N.S.

C.W.

NL

They all follow the form of the letters, then a number, then the year.

For example:

CW18099/19 a 1919 message

or CP13698/14 a 1914 message

The time period is pre-WWI through the 1930's (they may go later).

Does anyone know the meaning of these letter abbreviations and the reason one was used and not the other. The only one that seems clear is "M" which seems to be for messages that relate to 'movements.'

I would appreciate your help very much.