Long before the first email was sent or the first smartphone was designed, the blueprint for our modern digital world—from secure banking apps to private messages—was secretly being forged inside a 40-tonne machine humming deep beneath the footpaths of Queen Street, Brisbane City.
A Secret Below the Sidewalk
During the tense years of the Second World War, the AMP Building on Queen Street was more than just the headquarters for U.S. General Douglas MacArthur. In its basement, hidden from the world, Brisbane operated one of just twelve top-secret SIGSALY terminals on the planet. This wasn’t merely a telephone; it was the world’s first digital voice encryption system, a piece of technology so advanced that its principles are still used in the devices we carry in our pockets today.
The system was a lifeline, providing a completely secure, real-time voice link between General MacArthur in Brisbane and Allied leaders in Washington, D.C. While war raged in the Pacific, the strategic decisions that shaped its outcome were being discussed over a line that, to any eavesdropper, would have sounded like meaningless static.
The Birth of Digital Privacy
Developed by Bell Telephone Laboratories, SIGSALY was a marvel of its time. It took a human voice and, for the first time in history, converted it into digital data through a process called pulse-code modulation (PCM). This is the same fundamental method used today by everything from your mobile phone to music streaming platforms.
To make the signal unbreakable, the digital data was encrypted using a “one-time pad” system. Random noise was recorded onto large phonograph records, which had to be perfectly synchronised at both ends of the call. Each system filled an entire room, weighed over 40 tonnes, and required a dedicated team of trained personnel to manage its complex machinery. Despite constant efforts by Axis forces to crack Allied communications, no SIGSALY message was ever broken.
A Legacy Revealed
The existence of SIGSALY and Brisbane’s pivotal role in its network remained classified until the 1970s. Only then did the world learn how a wartime necessity had accidentally laid the groundwork for the information age. The innovations born in that Queen Street basement can be seen in modern encrypted messaging apps, voice-over-internet calls, and the secure networks that protect our daily digital lives.
This forgotten chapter of our city’s history was a key topic at an international symposium held at the University of Queensland. Scholars and historians gathered in August to examine how behind-the-scenes breakthroughs in communications and cryptography during the war, like SIGSALY, directly seeded the technology that defines the 21st century. The event highlighted that Brisbane’s contribution to the Allied effort went far beyond the battlefield, placing it at the very centre of a technological revolution.
Published Date 23-September-2025
