I explained back then what a GFT was and what it did, and it seemed like a good sort of title for something like a blog that delivers opinions and ideas like projectiles into the aether. I didn't talk about the other form of manual fire direction computation (as opposed to an actual computer, which was then and now the primary method of fire direction in use in the U.S. Army); this is a "Tabular Firing Table" or TFT, simply a book that contains table after table of information; this stuff includes things like corrections for wind, atmospheric pressue, temperature, elevation differences between the gun and the target, and barrel wear.
Eventually you get to "Table F", which, depending on projectile type, fuze type, and charge provides an elevation for the gun barrel and a setting for the fuze.
Anyway, the point of this post is that right now I'm reading the last of Rick Atkinson's "Liberation Trilogy", Guns at Last Light, and came across this bit of history buried in his discussion of the autumn battles along the German frontier:
"The shortfall partly reflected the inability of U.S. plants to meet demand: a 155mm shell required forty separate manufacturing procedures. The more common 105mm howitzer ammunition was produced and shipped under twelve hundred different lot numbers, each with minor variations in propellant that affected accuracy. (First Army was to spend 25,000 man-hours in the early fall sorting jumbled ammunition to avoid catastrophic short barrages."I was horrified when I read this.
One of the first things you get hammered into you when you learn fire direction is that you have to know the characteristics of your projectile and propellant. Changes in ammunition type, changes in fuze type, changes in propellant type can all have enormous effects on the point of impact of the round. Shoot a high explosive round using gun data calculated for an illumination round and you might sail hundreds of meters beyond your plotted target; shoot an HE round on data calculated for a white phosphorus round and it impacts tens or hundreds of meters short. Same with propellant. One lot might send the round 10% further than another, a third 10% less.
This is the great advantage of the modern ballistic computer. It can store data from hundreds of ammunition lots, freeing the fire direction crew from having to sort through all that shit.
But in 1944 the battery FDC's didn't have a computer. They had a bunch of guys, a chart board, and a bunch of TFTs.
The idea of trying to sort out twelve hundred individual ammo lots?
Gah. Gives me the shivers just thinking about it.
Anyway, the Atkinson book is damn good, worth a read for anyone interested in the period and the command and control issues of the Allied advance on Germany through Western Europe. Not a tactical primer but terrific on limning the times and peoples and giving you a sense of what happened and why.