33 USC § 3003
Authorized number on the active list
through Public Law 118-10
(a) Annual strength on active list
The annual strength of the commissioned corps in officers on the lineal list of active duty officers of the corps shall be prescribed by law.
(b) Lineal list
The Secretary shall maintain a list, known as the "lineal list", of officers on active duty. Officers shall be carried on the lineal list by grade and, within grade, by seniority in grade.