Under regulations prescribed by the Secretary, an individual, appointed as a Reserve officer, may be assigned a date of rank and precedence which reflects that individual’s experience, education, or other qualifications. For the purpose of this subchapter only, an individual appointed for the purpose of assignment or designation as a judge advocate in the Reserve shall be credited with a minimum of one year service in an active status. An individual holding a doctor of philosophy, or a comparable degree, in medicine or in a science allied to medicine as determined by the Secretary, may be credited with a minimum of three years service in an active status if appointed for an assignment comparable to that of an officer in the Navy Medical Department.