42 U.S.C. § 211c

Any medical officer of the Regular Corps of the Public Health Service who— (1) (A) was appointed to the assistant grade in the Regular Corps and whose service in such Corps has been continuous from the date of appointment or (B) may hereafter be appointed to the assistant grade in the Regular Corps, and (2) had or will have completed a medical internship on the date of such appointment, shall be credited with one year for purposes of promotion and seniority in grade, except that no such credit shall be authorized if the officer has received or will receive similar credit for his internship under other provisions of law. In the case of an officer on active duty on the effective date of this section who is entitled to the credit authorized herein, the one year shall be added to the promotion and seniority-in-grade credits with which he is credited on such date.