A Power of Attorney (POA) is a legal way to have a person act on your behalf. The POA gives someone else the right to act on your behalf on matters that you list in the POA.
A living will is an advance directive document. In some states, a living will may also be called a health care declaration or health care directive. It is an "advance" document because you state your wishes concerning medical treatment ahead of time. It is a "directive" because it allows you to choose medical treatments instead of family members or the hospital.
A living will can provide critical information to your treating physician at a time when you may be unable to communicate your wishes.
What if I am sued while on active duty? The Servicemembers Civil Relief Act (SCRA) can provide a 90-day stay (delay) of a civil lawsuit against you. You will need to ask the court for this delay. You may be able to do this with a letter, but you may need to file a form called a Motion for Stay of Proceedings
The Servicemembers Civil Relief Act (SCRA) provides several protection for active duty military members, including the potential to delay a lawsuit. However, a servicemember might want a case (such as a divorce) to move forward quickly and so they would like to waive that protection. It's possible to do that and you can read here for more information.