Was thinking of getting some new dog tags (with a "real" layout), thought I might share a few references here.
US Armed Forces typically carry two identical oval tags containing:
U.S. Air Force Format 1:
Surname, first name, middle initial
Social Security Number, followed by "AF" indicating branch of service.
Blood Group
"blank"
Religion
U.S. Air Force Format 2:
Surname
First name and middle initial
Social Security Number, followed by "AF" indicating branch of service.
Blood Group
Religion
U.S. Marine Corps:
Surname
First and middle initials, blood group
Social Security Number with no dashes and no spaces
Branch ("USMC"),Gas Mask size (S-small, M-medium, L-large)
Religious preference (or "NO PREFERENCE") or medical allergy if red medical tag.
U.S. Navy:
Surname, first name, middle initial
Social Security Number with no dashes or spaces followed immediately by "USN", space, blood group
"blank"
Religion (or "NORELPREF" if none)
U.S. Army:
Surname
First name, middle initial
Social Security Number
Blood type
Religion
Recently, the U.S. Army stopped using the term "Dog tags", replacing it with "I.D tags".
US Forces are also permitted to wear a small religious medallion, usually provided for them, on the smaller chain (e.g. a Cross or Star of David). This provides a quick, easily identifiable reference for a chaplain should his services be required.
US military ID tag ball chain specifications and lore
Standard US military chains are issued with one, 2.5 mm, 24-inch neck chain, and one, 2.5 mm, 4-inch duplicate chain. The secondary chain, and duplicate tag, are recovered if needed. The primary chain and tag remain with the soldier at all times.
Ball Chain may be upgraded to 3 mm diameter by individual soldiers. Chains smaller than 2.5 mm and larger than 3 mm are not generally authorized due to the risk of breakage/loss or inability to recover the duplicate tag from larger chains.
Prisoner of War time-keeping utility: Dog Tag Ball Chains were clipped to length to help captured soldiers count time in the event they were captured. The large chain was counted to 365 ball links and the small chain was counted to 52 ball links. A soldier could then bite, or break-off one link each day from the large chain, and remove one link from the small chain each week. This accounted for one year of time before the cycle consumed the chain completely. No verified comparison between the standard 24" and 4" chain lengths and number of "beads" per length has been performed. The typical length of 365/52 however, is adequate for mounting and wearing standard I.D. tags.
There are a few people on TradeMe that do tags, which I believe is where my original set came from + was really happy with them. One example is:
http://www.trademe.co.nz/Antiques-collectables/Militaria/Other/auction-313720433.htm
