Why is a former fighter pilot wanted by the US government?

"One man against the US, it's disgraceful," Daniel's wife Saffrine told 60 Minutes.

For 19 months, the former US Marine fighter pilot turned proud Australian citizen has been sitting in maximum security jail, accused of sharing top secret military information with China.

But that's nothing compared to the 65 years he could be locked up for, if the Americans get a hold of him and prove the father-of-six sold them out.

"It's a death sentence for my husband," Saffrine said.

"We will never see him again and my kids will never grow up with a father."

The US claims when the former Marine major was employed at a flying school in South Africa in 2012, he taught Chinese military pilots secret combat techniques, including how to take off and land on aircraft carriers. 

Homeland security expert Dr Charles Edel says the allegations against Daniel Duggan couldn't be more serious.

"The military is privy to secrets and they cannot trade those secrets away with foreign countries, with foreign competitors, with foreign adversaries," Dr Edel said.

"The last thing in the world that we want to do is make the Chinese military more capable, more adept at being able to fight."

Daniel Duggan always wanted to be a pilot, so he joined the Marines in 1990 and flew Harrier jets.

In 2002, his service ended and he moved to Australia.

Ten years later he became an Aussie, but curiously, instead of being a dual national, he gave up his American citizenship.

It was while living in Tasmania, he met and fell in love with Saffrine.

"Dan had an adventure company flying planes, and I was a photographer," she said.

"He was my Top Gun."

Life was good, but while running his business in Tasmania, Duggan also took temporary contracts to train pilots at a flying school in South Africa.

It's what happened there between 2009 and 2012 that the Americans are now questioning. 

Daniel said he only ever taught civilian pilots from China, but the US claims they were in fact Chinese military aviators.

Dr Edel said it's often difficult to separate the two.

"The Chinese have introduced a concept that they call civil-military fusion in how they go about acquiring technology," he told 60 Minutes.

"But it basically lays out the case that there is no distinction between civilian and military application and use."

"There is no bright shining line between those who are trained in the civilian arena and those who have the ability to actualize things from a military perspective when you're dealing with the Chinese state."

Speaking from inside his prison cell, where he's now been in solitary confinement for 569 days, Duggan argues the work he was doing in South Africa was all above board.

"I served honourably and proudly for 12 years," Daniel said. 

"There was not one time at any point where my oath to the Constitution was ever violated or in question, ever."

But America says as a former Marine fighter pilot, Duggan needed government approval - in the form of a state-approved licence - to do that kind of work.

Former UK Defence Minister Tobias Ellwood says his country has faced similar controversies with a number of former RAF pilots earning big money to help the Chinese.

As a consequence, he has little sympathy for Daniel Duggan.

"We are entering a dangerous era now," Tobias said. 

"It's absolutely adamant that anybody serving in the British armed forces, or the Australian or the American, you may leave the armed forces, but your loyalty to the nation must remain sacrosanct."

Suspicion only grew against Daniel in 2014, when he relocated his entire family from Australia to China, but Saffrine says there was nothing untoward about the move. 

"It was the place to be, there were lots of Australians going over there. Asia was a real hotspot," Saffrine said.

After six years, she and the kids returned home to Australia - but for Daniel, it wasn't that simple.

It's not clear why but the Chinese government confiscated his passport and didn't return it until September 2022.

Just a month after arriving back in the country, Australian Federal Police arrested Duggan in a supermarket car park in regional New South Wales.

"We didn't know for two months why he'd been arrested," Saffrine said.

"This is an innocent man, an innocent man that has no Australian charges."

On May 24, Daniel Duggan will learn whether he will be extradited to the US and face trial.

Tobias Ellwood said Duggan's case should act as a warning, as political tensions simmer around the world.

"China is growing in its military competence, certainly in its power, but it's not actually engaged in warfare," Tobias said.

"That's when you are truly tested."

It's one man up against the might of the United States government and the odds are not stacked in the former Marine major's favour.

Of course, the bid to extradite Daniel Duggan might fail and he could walk free.

More likely though, he'll be sent to America to face four charges including conspiracy and money laundering.

If found guilty, the 55-year-old faces spending the rest of his life in an American prison. 

"We will not give up," Saffrine said defiantly.

"I want to be proud that our Australian government does the right thing and brings Dan home."