§ 51. Retirement
(a)
An officer who, while serving in the grade of vice admiral, is retired for physical disability shall be placed on the retired list with the grade of vice admiral.
(b)
An officer who is retired while serving in the grade of vice admiral, or who, after serving at least two and one-half years in the grade of vice admiral, is retired while serving in a lower grade, may in the discretion of the President, be retired with the grade of vice admiral.
(c)
An officer who, after serving less than two and one-half years in the grade of vice admiral, is retired while serving in a lower grade, shall be retired in his permanent grade.
(d)
An officer serving in the grade of admiral or vice admiral shall continue to hold that grade—