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