What is rule 13 in the military?

There is no single, universally known “Rule 13” that applies across the entire U.S. military. The term is not part of the official Uniform Code of Military Justice (UCMJ) or standard regulations. However, the most common and widely recognized meaning of “Rule 13” in a military context refers to an informal guideline or unwritten rule within the U.S. Navy and U.S. Marine Corps.

In this informal tradition, Rule 13 is often stated as: “If it’s wet, don’t lick it.” This is part of a larger set of humorous, cynical, or brutally practical unofficial rules passed down among service members. These rules are meant to convey hard learned lessons about survival, avoiding trouble, and navigating military life with a sense of dark humor. Other examples include “Rule 1: The boss is always right. Rule 2: If the boss is wrong, see Rule 1.”

It is crucial to understand that this is not an official regulation you can be charged under. The real rules governing conduct are the UCMJ and service specific regulations. If you hear about a “Rule 13,” it is almost certainly referring to this kind of informal, unit specific folklore and not a legal statute.

For context on formal military entry requirements and standards, you can review information about ASVAB score eligibility.

For official information on the laws governing U.S. military conduct, you must refer to the Uniform Code of Military Justice (UCMJ).