(a) Except as specifically provided in regulations to be prescribed by the Secretary of Defense, or by the Secretary of Homeland Security with respect to the Coast Guard when it is not operating as a service in the Navy, each person who is enlisted, inducted, or appointed in an armed force, and who becomes a member of the Ready Reserve under any provision of law except section 513 or 10145 (b) of this title, shall be required, while in the Ready Reserve, to

(b) A member who has served on active duty for one year or longer may not be required to perform a period of active duty for training if the first day of that period falls during the last 120 days of the members required membership in the Ready Reserve.