In this FAQ, the subject of Cadets/Midshipmen/ROTC currently enrolled in SA's is answered as follows:
Q1.5. Will cadets and midshipmen at the service academies or in the Reserve Officer Training Program (ROTC) be given a choice between the BRS and legacy retirement system?
A1.5. Cadets and midshipmen attending a service academy as of December 31, 2017, will be grandfathered under the legacy retirement system and will have the option to opt into BRS upon commissioning.
ROTC cadets and midshipmen have the same option as long as they have signed their "contract" as of December 31, 2017.
Cadets and midshipmen that are grandfathered under the legacy retirement system, upon commissioning (or being placed in a pay status) after 2018, will have 30 days to decide to remain in the legacy retirement system or opt into BRS.
Each individual service member has a deadline, which is 30 days after their first day of duty following commissioning. Cadets and midshipmen who enter a service academy and ROTC cadets and midshipmen who sign their "contract" on or after January 1, 2018, will automatically be covered by BRS upon commissioning with no option to opt-in.