The date on the MWO (Modification Work Order) does indicate that it almost surely was for seatbelts.
OK what I'm about to write is from memory and research. I'm pretty sure it is correct but I can't be absolutely positive. Any corrections are welcome.
The "69" in the 7th and 8th character of the DLA (Defense Logistics Agency) contract number indicate that the contract was let in 1969. The truck may have been actually manufactured at a later date.
As for the serial number, the serial number breakdown for the post WWII M-series vehicles has changed several times but for the time frame of this truck, this should be correct.
The first two digits indicate the capacity of the chassis. In this case "05" indicates a 5 ton chassis. The "5" and "5 ton" are coincidental. Other truck capacities, in tons, do not directly correlate to the first two digits.
The 7th and 8th number of the serial number indicate the frame was serial numbered in 1971. Again the truck could have been delivered in a later year.
The 9th through 12th characters tell which number the truck was in a particular years production. When characters 10 through 12 got to 999 and then the letter in position 9 ("C" in this case) would go to "D" and the numbers would start over at 001. These numbers, apparently, did not "zero out" at the start of a new year so I don't believe them to directly correlate to the total annual production quantities.
The serial number was assigned to the frame at the start of the fabrication process and reflects when the frame was designated for a particular serial number in the contact sequence. The actual truck may have been delivered in a later calender year. In a few cases well over a year later. Also, "low density" and special purpose trucks sometime spent a lot longer in the fabrication process.
Occasionally you'll find a frame with one serial number X-ed out and a different number applied, (apparently before delivery) In all these cases that I can remember, the delivery tags had the superseding number so we figured it was changed by the factory folks not by any DOD agency.
This truck was the 128th chassis of the "C" series designated in 1971 to be built. The M819 has the same 215" wheelbase of the M812A1, M820/A1/A2, and the M821 trucks so the serial number probably falls into the same range as could be found on any of those chassis'.
Without the actual delivery date you won't ever be sure that the true delivery date was 1971 or 1972.
If dates seem to conflict try looking at the tranny, transfer and axles for dated makers tags or date stampings and see if there is any consensus.
The National Gurad has a searchable database that can tell the delivery or acceptance date for any truck that was in the system during the last few years. (assuming the owning unit's property book team was on the ball and did the data entry they were supposed to) I don't know if that database is DOD wide. If you are on really good terms with the maintenance folks at any Organizational level or higher maintenance shop (active duty, Guard or Reserve) they may be able to find something out.
Military Vehicles magazine had a great article some years ago on interpreting serial numbers, if you have a back issue library you might find it. I believe they have an online article database.
Hope this helps.
Lance
