R.I. Gen. Laws § 30-3-20: Relative rank of officers.

The date of the appointment of a commissioned officer of the national guard shall be expressed in his or her commission and shall be considered as the date thereof. Commissioned officers shall rank according to the date of their commissions. Between officers of the same grade and date of appointment, where there has been no previous military service, the relative rank shall be determined by age, the elder taking precedence. When two (2) officers of the same grade are commissioned as of the same date, their rank shall be determined first, by the length of previous service as a commissioned officer, second, by age, the elder taking precedence.