10 U.S.C. § 521: Authority to prescribe total strengths of officers on active duty and officer strengths in various categories

(a) Whenever the needs of the services require, but at least once each fiscal year, the Secretary of Defense shall prescribe the total authorized active-duty strength as of the end of the fiscal year for officers in grades above chief warrant officer, W–5, for each of the armed forces under the jurisdiction of the Secretary of a military department. (b) Under regulations prescribed by the Secretary of Defense, the Secretary of each military department may, for an armed force under his jurisdiction, prescribe the strength of any category of officers that may serve on active duty.