This is a list of heritage NATO country codes. Up to and including the seventh edition of STANAG 1059, these were two-letter codes (digrams). The eighth edition, promulgated 19 February 2004, and effective 1 April 2004, replaced all codes with new ones based on the ISO 3166-1 alpha-2 codes. Additional codes cover gaps in the ISO coverage, deal with imaginary countries used for exercise purposes, and designate large geographical groupings and water bodies. It consists of two-letter codes for geographical entities, four-letter codes for subdivisions, and lists the ISO three-letter codes for reference. The digrams match the FIPS 10-4 codes with a few exceptions.