A dog tag is the informal name for the identification tags worn by military personnel, because of their resemblance to actual dog tags. It is primarily used for the identification of dead and wounded along with providing religion (to provide for calling a Catholic Priest or Jewish Rabbi for Last Rites) and essential basic medical information for the treatment of the latter, such as blood type and history of inoculations.
Wearing of the tag is required at all times by soldiers in the field. It may contain two copies of the information and be designed to break easily into two pieces. This allows half the tag to be collected for notification while the other half remains with the body when battle conditions do not allow the casualty to be immediately recovered.