Which of the following is NOT a type of Navy correspondence?

The selection of "C" as the answer is correct because an informal note does not officially qualify as a type of Navy correspondence. Navy correspondence is characterized by its structured formats and specific purposes, such as conveying official information, instructions, or communications between personnel and entities.

On the other hand, types of Navy correspondence such as joint letters, multiple-address letters, and endorsements serve distinct functions within official communication channels. A joint letter is used when two or more officials need to co-sign a message, while a multiple-address letter facilitates communication to multiple recipients in a formal manner. An endorsement is a response or additional statement added to an existing correspondence to clarify or comment on the original message. Each of these types maintains a level of formality and adherence to procedural standards that is essential in military communication, which an informal note typically lacks. Thus, citing an informal note as correspondence highlights its distinction from the structured forms recognized in the Navy's correspondence guidelines.