"Dog Tags" serve a very simple primary purpose - identify dead bodies. Two tags were worn by each soldier. In the event of death, one was left on the body, and one was returned to the administrators to record the casualty.
The name ("ARTHUR K. FROST"), induction date ("6.3.18"), and branch ("USMC") were stamped on the face. The soldier's serial number ("4606475") was stamped on the back.
[This was rather a nice discovery. I have tried several times to obtain copies of Dad's military records from the archives, based on his name. Each effort was rejected with some (non-applicable) excuse form. According to other researchers', the key to actually getting a response is to provide them with the serial number. Apparently they are not inclined to do searches by name. I have high hopes of now being able to obtain his military record.]