You need to contact a competent attorney that knows DUI defense and how to handle the military aspect of this. If you are an outstanding soldier, you have a good shot at overcoming this and continuing your career.
Hiring a competent attorney sooner rather than later is the first step you need to take. Do so today.
Under AR 635-200, you may be involuntarily discharged for committing a "serious" military or civilian offense. For purposes of this regulation, a "serious" offense is one that would subject the soldier to a punitive discharge under the UCMJ. Although a first-time DUI without personal injury or property damage is a misdemeanor in most jurisdictions, if charged under the UCMJ, it would subject the member to a bad conduct discharge. See Manual for Courts-Martial, paragraph IV-35e(2). Thus, for purposes of discharge, it could be considered a "serious" offense.
Whether you can defend against the discharge action depends on a variety of factors. First, procedurally, if your command pursues an OTH service characterization, you will be entitled to a hearing before a board of officers, at which you may be represented by counsel, present evidence, and call and cross-examine witnesses. This is very similar to a trial. Also, if you have more than six years of active service, you will be entitled to a hearing regardless of your commands service characterization recommendation. If you have less than six years of service and your command pursues honorable or a general service characterization, you will not be entitled to a hearing, but may submit written materials in your defense to the separation authority.
Second, the particular circumstances of your case will weigh heavily in the outcome. This may not be the case, but I am assuming your DUI was handled in the civilian courts and that disposition is complete, i.e. you were found guilty or admitted to sufficient facts and punished. Your case will be much better if this is your first DUI and there was no personal injury or property damage involved. I find it odd that the Army would be pursuing discharge under such circumstances, but there is a lot of pressure on the services today to release people when possible. So all the services are making quality cuts when they can. If this is your second or greater DUI, or if there was personal injury or property damage, the chances of getting a favorable outcome will be significantly lowered.
In any event, you should seek counsel through TDS or hire a civilian defense counsel who knows military law. If your goal is to stay in the Army, then you should not try to go about this alone.
Answers to posted questions are for general interest only and do not constitute legal advice. No attorney-client relationship is established by virtue of any answer posted by the attorney.
You can fight it by requesting a separation board. Here's your problem, have you been in the military for over 6 years? Because if you have not, then you cannot request that a separation board be convened unless your unit is chaptering and seeking an OTH (or other than honorable) discharge. You have not provided sufficient facts, but my guess is that your unit is not trying to chapter you out with an OTH for just 1 DUI. Your unit likely intends to characterize your discharge as General, Under Honorable Conditions. If this is the case, then you need to have served for over 6 years in order to request a separation board. Going before the board and calling character witnesses in your favor is probably the best way to fight the chapter. Now, if you do not qualify for requesting a board, then I would suggest supplementing your chapter packet with a written statement either produced solely by yourself, or by a lawyer. Most detailed JAG counsel will not assist with drafting such statements due to their work loads. Include a memo for the CG (who is likely your separation authority), requesting that you be retained and that the separation proceedings be terminated. In the alternative, at least request an Honorable Discharge. Along with the memo, you should include a Soldier Achievement (or I Love Me Book) detailing your awards and achievements in the Army. Based on what information you provided, it sounds likely that a separation board would retain you despite the DUI.
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