Worth reading — Alan Turing's secret Delilah project

Sun, 21 Jun 2026 18:32:23 +1000

Alan Turing taught himself electronics from an RCA vacuum tube manual on a ship crossing the Atlantic in 1943. Within months he was in a Nissen hut in the English countryside, building a working voice encryption device that shrank a 50,000 kilogram Bell Labs room-filling machine down to three shoebox-sized units.

Donald Bayley was a young electrical engineering graduate who arrived at Hanslope Park in 1944. He found Turing’s soldered circuits looking like a “spider’s nest” and promptly dragged him through breadboarding boot camp. In return, Turing gave Bayley a series of evening lectures on advanced mathematics - and Bayley filled a school binder with notes. That binder, 180 pages of maths for circuit engineers in Bayley’s hand, is described as the jewel of the collection.

Bayley was also the reason any of this survived at all. He kept the papers for 66 years after Turing’s death, until his own death in 2020. The “Bayley papers” - notebooks, loose sheets of calculations scrawled on the backs of Army radio intercept forms, and that binder - were auctioned in London in November 2023 for almost half a million dollars. IEEE Spectrum got exclusive access before the sale.

What they reveal is Turing the electrical engineer: a side of him mostly hidden behind the code-breaker legend. A year after the breadboarding boot camp, the pair were testing the finished Delilah machine on a recording of Winston Churchill’s voice.

It’s a 13-minute read. Worth it.

The lost story of Alan Turing’s secret “Delilah” project — Jack Copeland, IEEE Spectrum, February 2025

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Worth reading — Alan Turing's secret Delilah project