If you are being assigned to Germany (permanently, not tdy, tad, or leave) as an active duty member, you have to register the firearm.
If by some chance you do take the firearm, you need an import form from the BATF to bring the firearm back to the US to show customs.
C3's advice should be heeded.
"A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
Life Member NRA
Life Member NAHC