You have been given a lot of good advice below. The most important step is the first one: take stock of your options (short sale, yes; HAP if military transfer, yes; etc), assemble a short sale package (a qualified local experienced Realtor can help you with this) and get the process started.
The longer you wait, and the more payments you miss, the more likely you will be forcing yourself into a position you don't want to be in.
Contact several of the Realtors who answered your question and ask them specifically about their success ratio with short sales, and their recommendations for YOUR specific circumstances to get a comfort level of who you would like to work with. This is a team process, with you and the Realtor hand in hand, so you need to be comfortable, as the short sale process involves copies of your financial history (paystubs, tax returns) for the last two years, and these require updating. You must feel 150% comfortable with the person you choose!
I hold several credentials in short sales, such as the Loss Mitigation Certification (LMC), Short Sales, Foreclosures, REO's (SFR) and Certified Distressed Property Expert (CDPE), and can help you with the process.
Good luck -
Prudential Network Realty