Delilah reunited with Turing's original papers at Hanslope Park

A working rebuild of Alan Turing's speech encryption system, Delilah, has been demonstrated to HMGCC staff at a special onsite event. It was shown alongside some of Turing and Don Bayley's original notes on the device.

It was the first time the working model and the original papers had been in the same room. The papers were also back at Hanslope Park for the first time since 1975.

Patricia McGuire, archivist at King's College Cambridge, brought the papers for display, together with other papers and correspondence of Turing. The Delilah papers, which belonged to Don Bayley, were auctioned in 2023 and sold to an overseas bidder. They were placed under a government export bar to give a UK institution the chance to buy them and King's College Cambridge acquired them in 2025, with significant financial assistance from public and private donors.

Delilah has its roots in a visit Turing made to Bell Labs in the United States in 1943. There he saw SIGSALY, a speech encryption system that introduced many firsts in communications technology. By the time Turing returned to the UK, he had conceived the idea for a smaller, more portable secure speech system of his own.

Working with Bayley, Turing succeeded in building a working prototype by the end of the Second World War. The pair demonstrated it to high-level visitors, often by playing a recording of a Churchill speech through the system to show it in action.

At the end of the war, Delilah was abandoned and the prototype destroyed, as priority shifted to other projects.

Rebuilding Delilah at HMGCC

Decades later, a team of volunteers led by John Harper set out to recreate it. HMGCC has supported the Delilah Rebuild Project in recent years, working from Turing and Bayley's original notes. HMGCC's historian has also reviewed the papers, to see what more they reveal about Delilah and how that could help the rebuild.

The historian said:

"The design of Delilah is highly innovative, applying knowledge that was not even in the textbooks of the day, and it pushed the limits of the technology available at the time.

"Testing the rebuilt Delilah has been quite a challenge, even given the advanced test equipment available today, which has let us see exactly what the circuits are doing."

Watch our video to find out more about Delilah: