General Discussion

Here is a short version of what the UCMJ
Disobeying an Illegal Order under the UCMJ

The Uniform Code of Military Justice (UCMJ) requires service members to obey lawful orders. However, it also makes clear that unlawful orders are not binding and must be disobeyed.

Relevant UCMJ Articles

Article 90: Willfully Disobeying a Superior Commissioned Officer – applies only to lawful commands.

Article 91: Insubordinate Conduct Toward Warrant Officer, NCO, or Petty Officer – limited to lawful orders.

Article 92: Failure to Obey Order or Regulation – covers lawful general orders, regulations, or directives.

What Makes an Order Illegal?
An order is unlawful if it:

Requires the commission of a crime (such as torture, targeting civilians, falsifying records).

Is beyond the authority of the person giving it.

Is manifestly contrary to the Constitution, U.S. law, or the laws of war.

Duty to Disobey
Military law and precedent make clear that service members have both a legal and moral duty to disobey unlawful orders. Carrying out such orders can result in criminal liability for the subordinate. Refusing a truly unlawful order does not violate Articles 90–92.

Historical Example
In United States v. Calley (My Lai Massacre, Vietnam War), Lieutenant William Calley argued he was following orders to kill civilians. The court rejected this defense: orders to commit war crimes are manifestly illegal and must be disobeyed.

Summary
The UCMJ requires obedience to lawful orders. If an order is illegal, a service member has a duty to disobey it. Obedience to such orders is not a defense and may result in prosecution.