JAGs must be licensed to practice law in at least one US jurisdiction (Illinois in my case). In the civilian world, only an attorney licensed in your state can give you legal advice. However, a special law, 10 USC 1044, allows JAGs to provide worldwide legal assistance, and mandates that states give full effect to the wills, healthcare directives, powers of attorney, and notary services we provide.
Most of my military estate plans were for couples, and I would commonly provide eight to ten documents at the end of an appointment -- everything from wills to trusts to community property arrangements, durable powers of attorney, living wills, and advance funeral directives. JAGs are happy to provide these services at no charge, saving our fellow military members thousands of dollars in legal fees.
Additionally, note that JAGs may be intimately familiar with common military estate planning issues, like owning property in multiple states, having domicile outside one's state of residence, and having one's family spread in jurisdictions across the country or the world. JAGs also commonly insert clauses in estate planning documents designed to express military members' wishes regarding burial in VA cemeteries, burial with full military honors, etc.
One note of caution: I have observed over the years that deploying military members may be quick to request a general power of attorney from the legal office. A general power of attorney grants the appointee the legal power to make transactions on behalf of the grantor. If the document is drafted to be "durable," it continues to remain in effect even if the grantor becomes incapacitated due to a combat injury or other medical condition. I understand people's reasoning for wanting these documents: Once a military member deploys half way across the world, the last thing he or she wants to be worrying about is taking care of day-to-day financial issues back home.
However, be aware that a general power of attorney can be used to empty a bank account, sign up for new accounts, sell a car, etc. Giving this kind of power to the wrong person can destroy your finances, your career, and worse. A JAG may be able to direct you to more appropriate tools to accomplish your objectives, like a narrowly-tailored special power of attorney (or no power of attorney at all).
Finally, note that you are not limited to legal assistance services from just your branch. During my years of service, I helped Airmen, Soldiers, Sailors, Marines, dependents, and veterans alike. A JAG from your nearest legal office can assist you with your estate plan.
Some useful links are below:
Air Force Legal Assistance
Army Legal Assistance
Navy-Marine Corps Legal Services
Coast Guard Legal Assistance
American Bar Association Pro Bono Resources for Veterans
Note: The information above is not legal advice and is not the basis of an attorney-client relationship. If you need assistance, you can hire an attorney to assist you with your individual legal needs.