For those with a keen mind for history, the recent Chinese spy balloon controversy may have reawakened some distant memories of Australia's Cold War-era balloon program.
While it was officially "secret", everyone knew about it.
More than 60 years ago, Australia and the United States launched the Hibal (High Altitude Balloon) project as a way of keeping tabs on weapons developments in other countries.
Not by flying over them, but by testing the air at extremely high altitudes.
It was a bit like sticking your nose out of the top window of your house to smell what the people three doors down were cooking.
The Americans figured the air from nuclear testing sites in the Pacific would waft across to Australia, carrying tell-tale particles with it.
Steven Thorn worked on the program in its early years and has since written his own book on Hibal, which was based in the regional Victorian city of Mildura.
"The Americans were sniffing at other people's weapons. They were interested in the French [nuclear testing] out in the Pacific," he said.
"The Americans had trace elements in their bombs and they could determine from the type of residue whether they were a hydrogen bomb or an atom bomb so I suspect that was part of the 'secret' part of it."
The balloons themselves were huge, reaching up to 100 metres in diameter.
They carried a 300 kilogram payload of atmospheric testing instruments to altitudes of more than 30 kilometres — well above the level at which commercial airliners fly.
The payload looked like something straight from the set of an old Dr Who episode, with visible wires, tubes and funnels all secured in place with what looked like sticky tape.
The project may technically have been classified top secret, but plenty of people knew about it — in fact, people used to come and watch the huge balloons being launched.
But it was the data captured high above the ground that was definitely off limits.
A race to reach the balloons as they crashed to earth
Launching the massive balloons was the easy part. Retrieving the payload wasn't always so simple.
The people working on the project had to track the balloons as best they could from an aircraft and give directions to a crew on the ground, who had to collect the payload from where it crashed to earth.
"Often the recovery crew were trying to get there, maybe the payload was being dragged by its parachute faster than they could drive out," Steven Thorn said.
"There was a lot of power and batteries on board so it could start fires if the batteries shifted around in the payload."
There was always a risk that the payload could crash through the roof of a house or come down in a dam, but most of the time they came to rest in a farm paddock.
Hundreds of the balloons were launched over the 15 or so years that the project ran.
Most payloads were recovered but there were reports of some balloons washing up in New Zealand or floating off as far away as Queensland.
Steven Thorn remembers the thrill of the chase as recovery teams raced to collect the payloads and placate any farmers whose crops may have been damaged by a falling 300 kilogram contraption.
"I had lot of good memories of being out flying and of the camaraderie with the crew," he said.
"In those days it was different, I mean you could stop at a pub on the way back."
A potential air disaster averted
The balloon launches didn't always go according to plan, as former air traffic controller Cass Alexander recalls quite vividly.
Mr Alexander was on duty one day in September 1976 when it became apparent to him that one of the HIBAL balloons was on a potential collision course with a Singapore Airlines passenger jet.
"It would be catastrophic. For example if the wingtip of the aircraft hit the payload it would just rip the whole wing off," he said.
Mr Alexander ordered the balloon be cut down, but encountered some resistance from the HIBAL team.
"I was aware of the legal situation I found myself in under the air navigation regulations at the time. You had to prevent collisions between aircraft, it was a legal mandamus [court order]," he said.
"I said 'listen this is a recorded conversation, I'm the controller responsible for this airspace, I'm ordering you to cut the balloon down now. if you do not, you bear the legal responsibility for any adverse outcome'."
The balloon and its precious and expensive cargo came down and thankfully the airliner continued safely to Melbourne.
Later, Mr Alexander was asked to recount the story to an arbitration commission as air traffic controllers made a successful push for a pay increase.
The HIBAL project petered out in the late 1970s as the Americans lost interest in sniffing our air, or found better ways of keeping tabs on their nuclear rivals.
It was rumoured that the plastic used to make the balloons became highly prized for lining dams on farms in Victoria's north-west where the contraptions came down.
Some of it might still be there to this day.
