Two fundamental facts – that soldiers in the field like to receive mail and that armies move, lead to the development of numbered post offices for military postal services. Add to those the value of anonymity of location for security. The practice did not begin in the United States or during World War II. It goes at least as far back as the Franco Prussian war in the 1870’s. The United States employed a system of numbered army post office during its role in the First World War.
The system of A.P.O.’s that serviced the army and army air corps during the Second World War began before the American entry into the war, and continues with some modifications through today. In the spring of 1941, President Franklin Roosevelt entered into an agreement with the government of the United Kingdom to exchange 50 destroyers for 99 year leases to establish military bases in several British Caribbean colonies. Army Post Office numbers were assigned to each of these new bases as the troops arrived to garrison them. The number of American servicemen stationed outside the boundaries of the continental United States increased during late 1941, and so did the number of A.P.O.’s. With the attack on Pearl Harbor, and the entry of the U.S. into the war, a full system of numbered A.P.O.’s was established.
In some cases there was a logical reason for a certain A.P.O. number to be used. For example, A.P.O.’s assigned to service infantry divisions were in most cases numbered the same as the division. The 1st Infantry division was assigned A.P.O. 1. In other cases, the A.P.O. number coincided with a regiment number. Certain geographic areas were assigned a series of numbers. For example, numbers 825 through 837 were assigned to specific bases in the Canal Zone, numbers 931 through 949 were assigned to Western Canada and Alaska, and numbers 950 through 966 were assigned to Hawaii. There were also other relationships between the A.P.O. number and sort of soldiers the A.P.O. serviced, but many A.P.O. numbers appear to have been assigned numbers on a random basis. In all, about 1000 different A.P.O.’s were in use the period between 1941 and the end of 1945.
[This overview of APOs was written by Jim Forte for his Postal History site and is replicated here with permission.]
