A former secret wartime laboratory and military headquarters that was ''camouflaged'' as a house has been listed by the National Trust, acknowledging its little-known role as the birthplace of radio astronomy.
The cliff-top structure formed the heart of Sydney's coastal defence system during World War II, serving as a central observation and command post.
After the war, scientists stayed to investigate a mysterious static that had plagued radio operators. They built an antenna by digging a giant hole in the earth, and used it to pinpoint the Milky Way's centre.
The building at the site, which has since been cement rendered and painted, was built with decorative, art deco touches to hide its real purpose, said a National Trust industrial heritage expert, Tony Brassil.
''They have laid everything out so - especially from a distance - it looks less like a military building,'' he said.
The property, built in 1938, has since been converted to a home.
During the war, CSIRO scientists working with the military to test new radar technology at the site noticed a strange radio interference, which was attributed to enemy action.
At the end of the war, they investigated and found it was coming from noise bursts linked to sun spots and flares.