The US Civil War was the first war in which US soldiers found the need to identify themselves in case of their death knowing as they did that they had a high chance of dying and that it could be days, weeks or months until their bodies were recovered. On both sides in the American Civil Ware soldiers used paper pinned to their tunics to identify themselves and who their families were and where they were.
The US started using dog tag style identification officially in 1906: the first major war in which it was used then was the First World War where other forces including Britain and her commonwealth were already using dog tags.
The First World War American Dog Tags necklaces were aluminium already but were at that time round, they included the regiment or corps of the wearer and only one tag was worn rather than two at first. It was in 1918 that the serial number system was first created and from then onwards a dog tag included a serial number to make positive identification much easier as each number was unique.
During World War Two there were three main different types of dog tag necklaces used in the US Army, which were now the familiar rounded rectangular shape. The first design was used from 1941 through to July 1943. The details on the first included as well as name, serial number, tetanus date and blood type, the name and address including city and state of their next of kin followed by their religious preference. The latter two designs had no next of kin information, either name or address, and the third version from March 1944 onwards changed the name order from first name initial and surname to surname, first name, initial.
For the Korean war the main change to the dog tag necklaces was that the US Army now gave a code as a prefix to the service number showing what type of solider wearers were. O was for officers, RA regular army, NG was National Guard and ER enlisted reserve with US for an enlisted draftee.
The Vietnam War is probably the war dog tags are most associated with despite their long history. Many films about the US in the Vietnam War include dog tag necklaces either to add authenticity or as some part of the story. The dog tag had a few details added by or during the Vietnam War; an army area was included for the first time to show which area a soldier was from. From 1968 onwards a social security number as well as a serial number was included, dog tags would sometimes use the serial and social security number and sometimes one or the other until June 1969 when all dog tags used the social security number only. The way religions were included was also different during the Vietnam War, before there were four codes for Protestant, Catholic, Jewish or no preference. During the Vietnam War religions would be written out and often gave more detail including specific denominations such as Baptist. Since June 1969 US Army Dog Tag necklaces haven’t changed and still use the social security number of the wearer rather than a serial number.