While you serve on active duty you can keep the license plates issued by your home state instead of registering in Massachusetts, as long as your insurance meets Massachusetts requirements. If you become a Massachusetts resident you have 30 days to register here. If your vehicle has U.S. Armed Forces plates you can drive it for up to 30 days when travelling to military duty or to your home.
There is nothing to apply for while you keep your home state plates. If you become a Massachusetts resident, register your vehicle at a Registry of Motor Vehicles location within 30 days.
Your out-of-state registration, proof of insurance meeting Massachusetts requirements, and your military orders.