The series consists of general correspondence and correspondence classified to 'Confidential', the Confidential files being held in green covers but interfiled with non-classified files. 'Secret' files were registered into a parallel classified series (CRS B5573).

There is also a close relationship between this series and the parallel secret correspondence series, in that papers were often initially registered as general correspondence but subsequently re-registered into the secret series, and sometimes the reverse applied.
 
Subjects are wide ranging and include all administrative matters as well as matters such as censorship, statistics, ships trials, Parliamentary, prosecutions, intelligence, lighthouses, conferences, discipline, British possessions, etc.  

The series was created by Navy Office in January 1922, after the abolition of the Department of the Navy in December 1921 and before its files were absorbed into the general Defence registry system in 1923. Thus this series only lasted 15 months before being replaced by another multiple number system (CRS B4883), which was closely modelled on the classification system used within Defence.
 
The use of a multiple number system by Navy Office was recommended by the Royal Commission into Naval Administration in its Report of 1918, but it was only when Navy Office was returned to the Department of Defence that the annual single number system in use under the Department of the Navy was abandoned.
 
By that time the de-centralized registry system instituted in Navy Office and in use from 1913 on, had also been abandoned in favour of a centralized registry system, and the files of all Navy Branches, except those of the Directorate of Naval Reserves and Mobilization, had been absorbed into the central Navy registry. However files in this series continued to be allocated alphabetical prefixes according to their subject category and corresponding to sections within registry roughly equivalent to the previous Branch divisions:

 N   Naval
 P   Personnel
 C   Civil
 S   Supply
 A   Accounts, and
 SC  Security classified correspondence.

The prefixes were discounted for filing purposes. They are present as part of the registry stamp placed on the top right-hand corner of correspondence, to which the file number was added. The lists of files transferred to the National Archives along with the records did not show the prefixes, and all items were entered into the database without the prefix.
 
The allocation of numbers to subject classes was done in alphabetical order, with the exception of those subjects relating to finance matters which were allocated the numbers from 1/- to 54/-. Other subjects were then allocated numbers from 101/- to 468/-. Many files have earlier papers from the 1911-1921 'Docket' system (CRS B2882) top-numbered into this series. Similarly, many files from this series can be found top-numbered and attached to papers in the subsequent series (CRS B4883). For some reason, the class of files relating to 'Ratings'(349/-) was continued in the subsequent series without top-numbering. Registers for class 349/- were also added to the subsequent control series (CRS B1125) and continued in use.  

The records in MP525/1 are part of Commonwealth Record Series B5572, Correspondence files, multiple number series, but have not been physically converted to B5572. The records should be requested under the MP525/1 number. The other physically unconverted element of Commonwealth Record Series B5572 is MT574/2, Defence (Navy) correspondence files relating to personnel matters, 1922.


Administrative information
 
The following data was keyed from the paper documentation:
Form number:              CA 17
Creating department:      Defence, Navy Office, Registry and Records
                          Branch
Transferring department:  Navy, Navy Office, Registry
Date of transfer:         03/05/1961
Archives file number:     RWM31/2/22