No, a defense counsel in a court-martial generally cannot file an “interlocutory appeal,” which is an appeal of a judge’s ruling made in the middle of a trial before a final verdict is reached. The military justice system, like the federal civilian system, has a strong policy against piecemeal litigation. The trial is meant to proceed to its conclusion without being interrupted by appeals of every ruling the judge makes.
When a military judge makes a ruling during the trial that is unfavorable to the defense, such as denying a discovery request or admitting a contested piece of evidence, the defense attorney’s recourse is to make a formal objection on the record. This “preserves” the issue for a potential appeal later on. The trial will then continue. The defense cannot stop the trial to immediately appeal the judge’s ruling to a higher court.
The proper time to challenge the judge’s ruling is after the court-martial is over and if the service member has been convicted. As part of the post-trial appeal to the service’s Court of Criminal Appeals, the appellate defense attorney will then raise the judge’s discovery denial as a specific error. They will argue that the judge’s ruling was incorrect and that it prejudiced their client’s right to a fair trial. If the appellate court agrees, they can then overturn the conviction.