Zuse S1

In between the numbered Z machines, Zuse built two special-purpose designs for Henschel Flugzeugwerke. The S1 was finished in 1942 and had a single job: compute correction values for the wing surfaces of the Hs 293 glide bomb, work that otherwise tied up a roomful of people on the factory floor. Around 600 relays, fixed wiring, no capacity to compute anything else. It was the exact inverse of the Z3 — not a general machine but a tool embedded in a production line.

Its successor, the S2 of 1943, took the step that makes the story worth telling: analogue-to-digital converters wired straight to the measuring instruments, so the machine read the wing itself and computed without anyone keying in figures. That makes the S2 a defensible candidate for the first process control computer, roughly a decade before the term existed. Both machines were lost in the war, and Zuse got nothing out of them — they were contract work for a customer, not designs he owned.