An officer in the permanent grade of ensign shall be promoted to and appointed in the grade of lieutenant (junior grade) upon completion of three years of service. The authorized number of officers in the grade of lieutenant (junior grade) shall be temporarily increased as necessary to authorize such appointment.
33 U.S. Code § 3023. Promotion of ensigns to grade of lieutenant (junior grade)
(a) In general
(b) Separation of ensigns found not fully qualified