After what event can an accused not demand trial by court-martial?

An individual cannot demand a trial by court-martial after non-judicial punishment has been awarded because this process is meant to provide a means of addressing minor offenses and correcting behavior without resorting to more serious legal proceedings. Non-judicial punishment, often referred to as Captain's Mast or Article 15, allows commanding officers to impose disciplinary measures based on their authority. Once this punishment is imposed and accepted, the opportunity for a court-martial ceases because the non-judicial punishment serves as a resolution to the offense in question.

In contrast, preferring charges, completing an investigation, or requesting a lawyer are all procedural steps that allow for the continuation of due process and do not preclude a demand for trial by court-martial. Each of those actions can still lead to further legal proceedings, unlike the acceptance of non-judicial punishment, which finalizes the matter within the disciplinary framework.