A Sunshine Coast man has discovered his father was involved in unloading mustard gas on Australian shores during World War II, despite its ban after the World War I.

Key points: Poisonous gas in WWI accounted for 12 per cent, or about 16,000, of Australian casualties

Poisonous gas in WWI accounted for 12 per cent, or about 16,000, of Australian casualties The Geneva protocol in 1925 banned the use of poisonous gases but not their production or stockpiling

The Geneva protocol in 1925 banned the use of poisonous gases but not their production or stockpiling Australia imported and stockpiled poisonous gas in preparation for invasion during WWII

Geoff Clarke's father Robert served as a guard in the Royal Australian Air Force (RAAF), and was in his mid-20s during World War II.

Robert never spoke to his son of his experiences during the conflict and Robert died in 1992.

It was not until Geoff was at a music festival this year in Cooktown, on Cape York Peninsula, that he decided he needed to know more about his father's wartime role.

Robert Clarke had been stationed in the remote Cape York during the war to build an airstrip.

Geoff sent his brother a text while at the music festival to let him know he was talking to the history museum in Cooktown.

"My brother texted back and said, 'Interesting, Listen, there's a diary in Dad's briefcase that contains more information'," Geoff said.

"I've gone, 'What?' Unfortunately, I didn't know about it."

Sergeant Robert Oswald Clarke during World War II. ( Supplied: Geoff Clarke )

Hot, hard work unloading gas

Upon close inspection of the diary, Geoff found the entry that showed his father had unloaded a boatload of 800 tonnes of gas on Middle Arm Wharf near Berry Springs, in the Northern Territory, in 1944.

"So that's what got me interested," Geoff said.

"We know that this gas was potentially mustard gas, and we know that my dad was a sergeant in charge of military police, in charge of the convoy."

Sergeant Robert Clarke's diary during World War II refers to unloading gas at Berry Springs, in the Northern Territory. ( Supplied: Geoff Clarke )

Robert Clarke's diary entry reads:

"Living on bully beef, Berry Springs, NT 29.4.1944 Commenced work at 1230hrs today, unloading gas from boat, did not unload gas itself, (but containers). Will commence on gas itself tomorrow. Was working on wharf today, but am going down hold tomorrow, very hot and very hard work."

The use of poisonous gas in World War I accounted for 12 per cent, or about 16,000, of Australian casualties.

The Geneva Convention banned the use of poisonous gas to attack enemies following World War I.

But importing it, and using it in retaliation, was still allowed.

Australia's secret stashes of gas

Northern Territory historian and senior lecturer at Charles Darwin University Steven Farram said his initial reaction was disbelief, when he first heard of the diary entries.

"The suggestion that Australians actually had mustard gas and were prepared to use it in the Second World War, at first I just thought, 'No, that can't be right'," he said.

But after asking around, Dr Farram said he found a few people who were involved in researching the World War II poisonous gas reserves.

"There had definitely been mustard gas unloaded at Darwin Harbour and taken to a storage facility, which was south of the place where Geoff's father had actually unloaded it," Dr Farram said.

The gas was taken to a facility called 88 Mile, or more fully, 88 Mile Burrell Creek Chemical Warfare Depot and Camp.

"There is some remnants of the camp that had been built there, the storage facility, just concrete slabs and some old rusted drums and other things can still be seen there," Dr Farram said.

"But there's no signs that show it otherwise."

Old drums are scattered around 88 Mile Chemical Warfare Depot, Northern Territory ( Supplied: Craig Bellamy )

Dr Farram said the barrels of gas were no longer there.

"They took them to a certain location and mainly burnt it," he said.

The historian said the reason the gas had been accessed and stored was because there was a fear at the time that the Japanese were going to use gas against Australians.

He said the Japanese had been using gas during their invasion and occupation of China, prior to the declaration of World War II.

Okunoshima, a small island in the Japanese Inland Sea, hosted a poison gas factory during World War II. ( Supplied: Australian War Memorial )

"It was only as the Japanese were looking quite successful up in New Guinea that they [the Australian authorities] thought, 'We've got to do something about this'," Dr Farram said.

"They contacted their colleagues in the United Kingdom and they accessed for them some excess World War I mustard gas and sent it to Australia."

Grappling with the past

Geoff was initially hesitant about going public with the discovery of the diary entries.

"The first casualty of war is the truth and the second casualty is morality," Geoff said.

Geoff said the importation of the gas raised moral questions about using banned substances against an enemy.

Effects of the poisonous gases on soldiers included acute breathlessness and eye irritation, paralysis and chemical burns to the skin.

It left veterans with long-term injuries, damaging the upper and lower airways.

A male volunteer shows mustard gas burns, in experiments conducted by the Australian Chemical Warfare Field and Experimental Section. ( Supplied: Australian War Memorial )

"When I learnt the effects of this stuff in the First World War on the men in the field, I just find it unbelievable that anybody, any government organisation would consider using it at all," Geoff said.

"It's easy for me to sit here right now and say, 'Why would you, back in 1944-45, [when I am] not facing an enemy coming down from Japan?'

"But I just find it a strange way of living a life, that's all."

Geoff said the moral implications had context in the modern day.

"I think the history of the Second World War should be told and the fact that we were prepared to use this stuff in the Second World War needs to be told, and just be honest about it," he said.

Geoff Clarke's late father's wartime diary appears to confirm Australia was stockpiling poisonous gas during World War II. ( ABC Sunshine Coast: Janine Hill )

In a statement, a Department of Defence spokesperson said historical activities at the former 88 Mile World War II camp were the subject of previous commentary online and in the media.

"Defence has no further comment at this time," the spokesperson said.