Directives/Instructions – administrative documents that are cataloged by number. See here: http://www.dtic.mil/whs/directives/corres/writing/Issuance_Numbering.pdf
Establish policy, assign responsibilities, and delegate authority to the DoD Components--Do not contain procedures.
Can be signed by either the Secretary or the Deputy Secretary of Defense or by the Under Secretaries of Defense delegated the authority to sign.
Assign responsibilities; may contain overarching procedures.
Signed by OSD Component Head; Principal Deputy; or Presidentially-Appointed, Senate-Confirmed (PAS) Officials.
General Orders – Permanent instructions, issued in order form, that apply to all members of a command, as compared with special orders, which affect only individuals or small groups. General orders are usually concerned with matters of policy or administration.
Manuals – Implements or supplements a Directive or policy Instruction, which will be cited as a Reference; Provides detailed procedures for carrying out the policy in a Directive or policy instruction; May not establish policy.
Memos – Issued ONLY for time-sensitive actions and ONLY when time constraints prevent publishing a new issuance; May establish or implement policy.
Regulations/Pamphlets – administrative documents cataloged by subject into series that define a branch’s policies and procedures.