The Feldpost number was a five digit code number and by the end of 1939, letter prefixes "L" and "M" were attached in front of each FPN to units belonging to the Luftwaffe and Kriegsmarine. A breakdown by military units was added by attaching letter suffixes "A" through "E" at the end of each FPN. The letter A generally signified headquarters company, the others stood for line companies. The sequence of a Feldpost number did not necessarily mean that the location of the units were at the same area.