For offenders who were at the time of commission of their offenses subject to his authority and who merit such action, the Secretary concerned shall establish—

(1) a system for the remission or suspension of the unexecuted part of the sentences of selected offenders;

(2) a system for the restoration to duty of such offenders who have had the unexecuted part of their sentences remitted or suspended and who have not been discharged; and

(3) a system for the enlistment of such offenders who have had the unexecuted part of their sentences remitted and who have been discharged.