What is rule 13 in the military?

There is no single “Rule 13” that is an official, codified regulation in the U.S. military’s legal system, such as the Uniform Code of Military Justice (UCMJ). The term is most commonly encountered as part of an informal, often humorous list of “unwritten rules” shared among service members, particularly within the U.S. Navy and Marine Corps.

In this widespread informal tradition, Rule 13 is typically stated as: “If it’s wet, don’t lick it.” This aphorism is part of a larger set of cynical, practical, or joke guidelines meant to impart hard-learned lessons about survival and avoiding trouble in military life. Other examples from these lists include “The boss is always right” or “Never volunteer for anything.”

It is critical to understand that this is folklore, not law. You cannot be charged or disciplined under “Rule 13.” Actual military conduct is governed by official publications like service regulations and the UCMJ. If you hear a reference to Rule 13, it is almost certainly this type of unofficial service culture being referenced.

For insight into other military decision-making frameworks, you can read about the 10-10-10 rule.

To understand the official laws that truly govern military conduct, service members and the public should refer to the actual Uniform Code of Military Justice.