I didn't know where to post this and please feel free to remove if posted before, i found this info elsewhere and thought it would be useful to post if ever the link died!...
One of the most commonly seen features on United States Military Equipment and Clothing is a DA, DSA, DLA, or SPO Contract Number stamp. If you correctly read the stamp, you will know when your item was manufactured.
The first was DA, which stands for Defense Agency. It ran from 1953 to 1961. It was superceeded by the DSA, which stands for Defense Supply Agency. It was used from 1962 to 1977. After that, the DLA, the Defense Logistics Agency took over from 1978 to 1993. From 1994 to the present, the SPO - System Program Offices have been in charge of procurements.
If your item has a Manufacture's Stamp only - it was made prior to the beginning of the Korean War. A knowledge of when the particular item was used will narrow down the time frame. A date stamp may, or may not be present.
DA stamped items range from the Korean War to very early Vietnam War. Look for a two digit number, typically near the end of the code (it will range from 53 to 61) for the exact year of manufacture of your item.
DSA stamped items introduced a systematic dating process:
1962 thru 1964 - Prefix of DSA-1, Suffix of E6Y (Y=Year)
1965 - Prefix of DSA-1, No Dating Suffix
1966 - Prefix of DSA-100, No Dating Suffix
1967 thru 1977 Prefix of DSA-100, Dating Suffix of YYM (YY=Year, M=Month)
After the DSA Prefix, and before the Dating Suffix (if applicable), there may appear additional numeric or alphanymeric code(s). These codes have nothing to do with date of manufacture, but relate either the Defense contract, or a Manufacture's code.
The DLA continued the last DSA dating system, substituting DLA for DSA; for example: DLA-100-805 would indicatre an item made in May of 1980.
The SPO stamp has the year of manufacture as the first two number code following the initial 6 character alphanumeric code; ie: XYZ23A-05-xxxx would indicate an item made in 2005.