What you need to do
If your vehicle was purchased, titled, and registered in your home state, you may retain your home state registration indefinitely, regardless of where you are stationed in the country. The only requirement is that you carry insurance at least equal to Massachusetts minimum levels.
If your vehicle was purchased, titled, and registered in a state other than your home state, you will need to register the vehicle in each state you are assigned to. If you are not a Massachusetts resident and your vehicle falls into this category, you may drive the vehicle with the existing out-of-state registration for 30 days only. You must register and title the vehicle in Massachusetts before the 30-day period has expired.
If you are returning from service abroad and your vehicle bears plates issued by the Armed Forces, you may drive the vehicle for up to 30 days for the purpose of traveling to military duty or to your place of residence.