Which of the following are considered official Navy labels?

Official Navy labels serve to convey important information about equipment, supplies, and materials used within the Navy. These labels often contain specific identifiers that ensure proper handling, storage, and accountability.

The correct choice features a designation that aligns with the format typically used for Navy-related documentation or classification. Specifically, DD-2521 refers to a form or document used by the Department of Defense, which indicates it is an official designation within the Navy's administrative framework.

Other options may resemble Navy identifiers but do not conform to the established labeling formats used for official documentation. For instance, HE-X342 and HAZ-0021 do not represent official Navy label formats that are recognized for administrative or inventory purposes, while the NSN (National Stock Number) format is used for identifying items in logistics but does not represent the label itself.

Thus, selecting the option that accurately represents recognized official Navy documentation ensures adherence to established Navy procedures and organizational standards.