33 U.S. Code § 3004 - Strength and distribution in grade
Subject to paragraph (2), whenever a final fraction occurs in computing the authorized number of officers in a grade, the nearest whole number shall be taken, and if the fraction is one-half the next higher whole number shall be taken.
No officer may be reduced in grade or pay or separated from the commissioned corps as the result of a computation made to determine the authorized number of officers in the various grades.
Nothing in this section may be construed as requiring the filling of any vacancy or as prohibiting additional numbers in any grade to compensate for vacancies existing in higher grades.
The total number of officers authorized by law to be on the lineal list during a fiscal year may be temporarily exceeded so long as the average number on that list during that fiscal year does not exceed the authorized number.