This type of dog tag was used by the Graves Registration Service (QMC), when it proved impossible to determine the identification of an unknown soldier. In cases of group or individual casualties, either in aircraft crashes, burned tanks, or water casualties, where positive evidence of individual identities were completely lost and only group identities could sometimes be determined by organization lists showing the crew complement, it was possible occasionally to separate and preserve the individual remains of one or more and, in some instances, all the members of a same crew. When Identification Tags were missing, and all evidence of identification had been completely destroyed by fire or otherwise, bodies had to be definitely marked UNKNOWN, with designation X-6, or X-45, etc., i.e. the numeral assigned to the first body being the next serial number to the last UNKNOWN X-(number) remains already buried in the temporary cemetery where the remains were to be interred. The Grave Marker was then to be marked with an embossed plate, i.e. a substitute Tag, with the following data: UNKNOWN SOLDIER and X-224 followed by GRS. The dog tags would be nailed to a wooden white cross at a temporary grave site when the GI was buried.
Seen here is an unissued paper identification tag for a patient. These were meant to be affixed to medical patients aboard ships, so medical personnel would know the certain patient's diagnosis.