6000 series—Medicine and Dentistry 7000 series—Financial Management 8000 series—Ordnance Material 9000 series—Ships Design and Material 10000 series—General Material 11000 series—Facilities and Activities Ashore 12000 series—Civilian Personnel 13000 series—Aeronautical and Astronautical Material These major groups are subdivided into primary, secondary, and, at times, tertiary (third-level) subdivisions. Primary subjects are designated by the last three digits of the code number, secondary subjects by the last two digits, and tertiary subjects by the last digit. For example: 6224 6000 Medicine and Dentistry 6200 Preventive Medicine 6220 Communicable Diseases 6224 Tuberculosis 6100 Physical Fitness 6600 Dentistry D e t a i l e d s u b d i v i s i o n s c a n b e f o u n d i n SECNAVINST 5210.11. Classifying Classifying, as it is used here, is the process of determining the correct subject group or name-title codes under which correspondence should be filed and a n y s u b o r d i n a t e s u b j e c t s t h a t s h o u l d b e cross-referenced. Classifying is the most important filing operation because it determines where correspondence is to be filed. The proper way to subject-classify a document so that it can be readily identified and found when needed is to read it carefully, analyze it, and then select the SSIC that most closely corresponds to the subject. Cross-Reference Filing File most official correspondence, reports, or other material under only one standard subject identification code. There are times when more than one code will apply to the contents of the correspondence. In these cases, a system of cross-referencing is desirable to permit you to locate the correspondence quickly. To cross-reference, use a Cross-Reference Sheet, DD Form 334 (filling in the required information about the correspondence), or make a copy of the corre- spondence and place it in the appropriate cross -referenced file. Instances where you need to use a Cross-Reference Sheet are when  a document has more than one subject;  the subject may be interpreted in such a way that it lends itself to filing under more than one specific subject group;  two or more subject identification codes pertain to the names, places, or items appearing in the document;  enclosures are separated from the basic correspondence; or  oversize material is filed in an area that is separate from the file for which intended. Official Method of Filing Loose filing of correspondence in standard file folders is the official method because it saves time and material. A label containing identifying data for each folders contents is generally placed on the tab of the folder. Five-drawer, steel, non-insulated, letter-size cabinets are standard equipment in the Navy for filing correspondence and documents. Material that cannot be folded neatly in the intended file should be filed in a suitable cabinet. Note the location of this material on the basic document of a cross-reference sheet. Files containing classified documents or Privacy Act data are to be properly secured in accordance with the current version of OPNAVINST 5510.1. Use of computers to maintain files is also a quick method for retrieval. However, paper and/or backup disk copies of the computer files must also be available. Terminating Files General correspondence, as well as most other files, are terminated at the end of each calendar year, and new files are begun. Budget and accounting records are also terminated annually, but at the end of each fiscal year (30 September). Maintain terminated files in the office for 1 year before they are retired to a storage area where they are maintained until they are eligible for destruction or transfer to a Federal Records Center. The current version of the Disposal of Navy and Marine Corps Records Manual, SECNAVINST 14-5