Okay...from what I know/understand it goes like this. IF you are active duty and have had the car registered overseas and/or previously registered in the states PRIOR to shipping it back CONUS=US and trying to register it in MD then you can ask for exemption of the state sales tax. However you have to have had the car registered and driven overseas I believe for more then 6 months! That is to keep everybody from doing a Euro delivery in Munich and driving their cars for <30 days and then bringing them home and Uncle MD not getting any $$$ from their purchases.
Now I would preface the above statement in saying that I have NOT done this myself with my car. I was not able to pick it up and drive it overseas at all let alone long enough to satisfy that 6 month term. BMW-NA Military sales gave a handout on this somewhat somewhere when I bought my car and I'll see if I can find it BUT they too preface it by saying basically the state the car is registered in has the right to do what the hell they want to do! So I paid my sales tax and picked my tags up from my local dealer...it was a WHOLE lot easier that way as instead of the dealer you are listed as the importer and such on the customs forms and for title purposes and such it was a royal pain in the azz getting a straight anwser from MD DMV's websites. SO I cut a check to the dealer's tag dept and showed them all the paperwork of manufacture and ownership and they cut me a brand new set of hard tags and plates and I picked my car up at the PDC in SC.
Sorry to digress but in your situation the more info is probably the better for comparision sake. I'd call DMV and tell them what I was trying to do specifically explaining that you are mil/govt employee (you are I suspect) and are bringing your car back stateside and need to register it. You probably will need to show something proving that it WAS registered and you paid something in Germany when you got it; thus your request for exeption here. Get copies of everything!
Also Some ports by the way won't release the car to drive off the dock without tags so be careful of that too! I'd also call your local dealer too as they may have some insight too (I can ask around myself if I get a chance as my buddy is a senior CA and another the CPO sales manager at a dealer down the street from base).
Final option; ship and register it to a state you KNOW will not charge you sales tax. Also ask ShadyM3 as he did the same and picked his car up in GA and drove it to Tx and had a time with getting it...but am not sure if he had to pay taxes or not. Like I said each state is very different.
'14 Range Rover Sport SC (Chille/Black) - Mine
'15 BMW M3 (Black/Black) - gone but not forgotten
'16 Cayenne (Black/Black) - Herz
'13 Harley Davidson Dyna Custom - born to ride