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In 1994 I was a young US Army armor officer responsible for the maintenance of an armor battalion at Ft Hood, TX. It was a fun job, leading a team of 90 Army mechanics, and I was responsible for keeping our combat readiness very high. Seared into my memory to this day (25 years later) is a key piece of data - for a repair part. I still recall the national stock number (identification number) NSN 6140-01-210-1964. That was the ID for the storage batteries for our combat vehicles, which were roughly the same as a big car battery and were used to start our vehicles.
Why do I recall that meaningless string of numbers a quarter century later? Every combat vehicle had at least 2 of these batteries (M1A1 tanks had 6 of them) – so we had around 750 of these things in our battalion and as sure as the sun shone in Central Texas, those darn batteries would fail at the most inopportune times. Without working batteries our combat vehicles were inoperative and we would then race to try to get replacement batteries to make the vehicles operational in time for a field training exercise or gunnery exercise. That 6140-01-210-1964 was the magic ID key to the Army parts system to get the needed battery and get the vehicle(s) operational again. Usually it was at night, or raining (or both) and seemed like it was just before we were to start an exercise and needed all the vehicles working properly. It meant driving many kilometers to the repair parts depot on muddy trails (at night without headlights) – in hindsight that should have been a lot of fun but when you're tired it's not.
Now of course, sometimes a sleepy parts clerk ordered the wrong ID – and voila we got the wrong part, and that vehicle remained inoperative even after such a drive. Luckily, this was just peacetime training and soldiers' lives were not on the line - so we could learn from it and just suffer the wrath of an upset battalion commander whose readiness was lower than what he needed. In combat that could have been another matter altogether…