An unusual demilitarized slide rule
And they shall beat their swords into plowshares, and their spears into pruning hooks; nation shall not lift up sword against nation, neither shall they learn war any more.
– Isaiah 2:4
Like almost any human invention the slide rule has been applied to the waging of war, but I have one slide rule that made the opposite transition back to peaceful use.
This is a large (46 cm long) rule whose front side carries the scales for calculations related to the manufacture of steel springs. These scales are clearly handmade, typed up on paper with a typewriter and varnished with some transparent protective layer. There is no maker name or logo, nor any other hint to its origins – not on the front side, there isn’t. But flip it over, and you see a very different story.
The back of the stock shows some half-torn tables that seem to apply to artillery calculations; and the slide still has on its back the original scales in full, which show that this slide rule had to do with the M1 155 mm field gun. No mystery there: the stock is marked as a Graphical Firing Table M13, one of a family of artillery ranging rules made by Keuffel and Esser in the early 1940s. It is quite sturdy, as befits a military item, and has survived the years since its conversion in perfect functionality.
So what we have here is a rare – possibly one of a kind – postwar conversion of a WW2 gunnery calculator into an industrial calculator for steel spring production. There must’ve been many “Firing Table” slide rules that were no longer needed; evidently someone decided to repurpose the solidly constructed slide rule frame into a useful tool for their company, either to use as is or as a prototype for a final product (though I am unaware of such a product – I have a couple of commercial spring slide rules, but they both follow a different pattern).
Here are some close ups of the front side; the shillings cost scale points to a UK conversion, even though the substrate is US-made. Given the austerity of the post-war years in Britain, this makes sense.
Alas, Isaiah’s vision is yet to come; but this slide rule definitely embodies the concept of beating swords into plowshares!
Exhibit provenance: eBay, from a seller in the UK.
More info:
See here for more on the K&E Firing Table slide rules.