Your New York driver licence and vehicle registration stay valid throughout your military service and for six months after discharge or separation. After that you have a 24-month grace period, so you can renew an expired licence up to 30 months after separation. Vehicle registrations are extended for up to 60 days after you return to New York. If you hold a driver licence issued by the U.S. Armed Forces, you can drive in New York for 60 days after entering the state, after which you need a valid New York or out-of-state licence.
There is nothing to apply for while you are serving. When you return, show proof of your military service or separation at a DMV office to renew your licence or registration under the extension.
Proof of military service or your separation or discharge paperwork.