It's a scavenger hunt with a difference. An archaeological dig to discover the country's little-known military history. 

Amateur wartime historian Charles Tennyson and criminal lawyer Mark Rawson have started excavating a site at Nelson Bay, north of Newcastle, that they believe was a secret US military base during World War II.

After years of research, they are hoping to salvage equipment that was dumped at the end of the war.

While locations were often secret at the time, the two partners in Allied Salvage and Research believe there are bunkers and tunnels around the country that contain wartime planes, vehicles and possibly munitions and drums of mustard gas. 

"We know a good couple of hundred sites," Tennyson says.

They believe a man-made hill in a park at Fly Point, Nelson Bay, contains a former US Navy depot.

"We know for a fact it was a secret training area for amphibious landings," Tennyson says. "There were 22,000 US soldiers along with Australian soldiers being trained to attack beaches before setting off to the war in the Pacific.

"We have a diary that says there were 136 naval ships including four aircraft carriers in the bay on one day during the war."

Rawson says he was initially sceptical when he heard old soldiers talk about the US military burying equipment rather than taking it back home given the lack of official records. 

"Everyone was in such a rush to get home after the war," he says. "So it appears that, in a lot of cases, they simply found locations to dump this stuff then cover it over. We're talking the full gamut of what they had – arms, equipment, planes, jeeps, trucks, you name it."

While equipment buried in pits will have deteriorated badly, the duo believe other gear was stored in tunnels and concrete bunkers that could be worth salvaging.

"There are museums and collectors that would be very interested in some of this gear," Rawson says. "And the other side of the coin is it's still good Pittsburgh steel and it could be scrapped."

The partners have a personal connection to the Nelson Bay site. 

As a teenager during the war, Tennyson's late mother-in-law, Cecily Haddock, saw a tunnel entrance big enough to drive two trucks through.

After two years getting federal and local government approval to excavate, the partners have found a decayed US military jeep then hit concrete during early drilling. 

"What we expect to find is a whole heap of stuff that was simply ploughed into there at the end of the war," Rawson says. "You could be talking tents, jeeps, motorbikes, drums of fuel and anything that was lying around."

Even if there is little worth salvaging, they see the site as a potential tourist attraction. 

They also want to investigate:

• A site near Bankstown Airport where they believe fighter planes are buried.
• In Melbourne, a rumoured tunnel system under Royal Park that reputedly includes General Douglas MacArthur's main bunker when he became Supreme Commander of South-West Pacific Area in 1942.
• An army base at Bandiana near Wodonga, where houses have been built on the top of what they believe is an underground bunker containing wartime trucks in crates. 
• Townsville's Castle Hill, which has long been rumoured to contain old military tunnels with sealed-up barrels of mustard gas. And another site in the city they think contains Hellcat fighter planes. 
• A tunnel system at Mount Elliot, south of Townsville. 
• Tunnels at Bowen that reputedly contain Catalina aircraft.

The US military had up to 150,000 personnel in Australia during the war and established military bases largely in the country's north.

Tennyson concedes most people will be sceptical of their belief about buried planes and other equipment. 

"But when you look at the evidence and the number of eye witnesses, where there's smoke there's fire," he says.