can  be  found  in  OPNAVINST  4790.2  (series).  There  are two  types  of  TDs,  formal  and  informal,  which  are distinguished  by  their  method  of  dissemination.  They are  normally  distributed  as  technical  notes/orders, bulletins, or changes. The three action categories of TDs are as follows: .  Immediate.  This  category  is  assigned  to  TDs when an uncorrected safety condition exists that could result  in  a  fatal  or  serious  injury  to  personnel, destruction to valuable property, or serious damage. Compliance must be accomplished before returning aircraft or equipment to service. Kits/parts required in this  category  should  be  requisitioned  by  using  supply issue group I. . Urgent. This category is assigned to TDs when a potentially   hazardous   condition   exists   that,   if uncorrected, could result in injury to personnel, damage to  valuable  property,  or  unacceptable  reduction  in operational  efficiency.  Although  this  category  does  not remove aircraft/equipment from service, it does have a specific  date  or  time  frame  assigned  by  which  the  TD must be accomplished. Kits/parts in this category should be ordered by using supply issue group I or H, depending on the date assigned for completion. .  Routine.  This  category  is  assigned  to  TDs  when there  are  reliability,  capability,  or  maintainability deficiencies that, if uncorrected, could become a hazard through prolonged use or have an adverse effect on the life or use of the affected equipment. This category does not have specific compliance dates assigned. Kits/parts in this category should be requisitioned by using supply issue group III. SECURITY OF OFFICIAL CORRESPONDENCE The  security  identification  of  Confidential  or  Secret instructions and notices is indicated by prefixing the subject numbers by “C” for Confidential and by “S” for Secret. A single set of consecutive numbers is used for each   originating   office   for   each   subject   number regardless of the security classification of individual instructions. Example: If the first instruction issued on “material expenditure”  is  Unclassified,  the  second instruction  Confidential,  and  the  third  instruction Secret, they would be numbered 4480.1, C-4480.2, and S-4480.3,  respectively.  The  classification  designations of   information   that   require   protection   against unauthorized  disclosure  in  the  interest  of  national security are as follows: Top Secret: Unauthorized disclosure of Top Secret information  could  reasonably  be  expected  to  cause exceptionally  grave  damage  to  the  national  security. Secret:   Unauthorized   disclosure   of   Secret information could cause serious damage to national security. Confidential:  Unauthorized  disclosure  of Confidential information could reasonably be expected to cause damage to the national security. Documents marked FOR OFFICIAL USE ONLY (FOUO)  contain  information  that  should  be  disclosed only to persons who need to know to perform their official duties. For you, it means that you will disclose information only when and as directed by your superiors in the chain of command. Disclosure of information, which may be limited to official use, even though such material is not appropriately marked, is covered by Navy Regulations,  Article  1252. Security  clearances  for  access  to  classified  informa- tion are obtained after investigative requirements on the individual is completed. This also applies to the AKs handling  classified  material.  Regulations  and  guidance for classifying and safeguarding classified information and  for  personnel  security  for  DON  activities  and personnel are provided in OPNAVINST 5510.1. Classified  record  material  may  be  destroyed  only when  destruction  is  the  disposition  authorized  by SECNAVINST  5212.5.  all  other  classified  material should be destroyed as soon as it is no longer required. Early  disposal  of  unnecessary  classified  material  can assist  in  reducing  security  costs,  preparing  for emergency  situations,  and  better  protecting  necessary classified   material.   Classified   material   must   be destroyed only by authorized means and by personnel cleared to the level of the material being destroyed. The method used to destroy classified material must prevent later   recognition   or   reconstruction.   The   common methods of destruction are as follows: .  Burning:  This  is  the  traditional  method  of destruction.  The  destruction  is  complete  and  disposition of  remaining  ash  is  relatively  simple. . Shredding: This method can be done in two ways. In strip shredding, the machine must cut the material to be destroyed into strips no greater than 1/32 inch in width. In cross-cut shredding, the machine must reduce the material to shreds no greater than 3/64 inch wide by 1/2 inch long. 2-10