Under regulations prescribed by the Secretary, a person, appointed as a Reserve officer, may be assigned a date of rank and precedence which reflects that person's experience, education, or other qualifications. For the purpose of this subchapter only, a person 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. A person 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.