A hidden tunnel, which is part of Australia's wartime history, has been uncovered, by road maintenance workers at Waterfall in Royal National Park.
Transport for NSW Sydney maintenance director David Fishburn said the tunnel under McKell Avenue, one of the main access roads to the park, was part of a network of small explosives chambers, prepared in 1942 in case of invasion during WWII.
"We understand the chamber was dug under the road so that explosives could be hidden within it,' he said.
"In the case of an invasion, the explosives would have been detonated and the road destroyed to hinder the progress of enemy troops.
Mr Fishburn said the explosives had since been removed and in their place was a colony of regionally significant microbats, known as the Eastern Horseshoe bat.
"Records of road blocks laid in 1942 identify four such tunnels within the Waterfall area, including this chamber, also known as an 'adit', on McKell Avenue," Mr Fishburn said.
"It's believed there could still be around 40 others in the Illawarra region.
"The Royal National Park was considered an ideal location for the defence of the Sydney coastline in the Second World War."
Mr Fishburn said the discovery was made while workers were investigating planned slope stabilisation upgrades on the road.
"The chamber is about seven metres long and 1.2 metres high, only accessible by rope and lined with sandstone blocks, with additional timber supports which appear to be collapsing and eroding," he said.
"When the adits were decommissioned, stone walls were to be built across the openings, but either this wasn't done, or the wall has collapsed away without trace."
The planned work, which is designed to ensure the road remains stable for motorists for years to come, will include the installation of rock bolts, drains and sealing the adit.
Mr Fishburn said Transport for NSW and its contractor Ventia Boral Amey would work closely with environmental experts and a specialist ecologist to ensure any work minimised impact on the bats.
WWII and Sutherland Shire
Information provided by Transport for NSW
During 1942, the threat of an invasion of Australia appeared imminent. 10 weeks after Japan's invasion of South-East Asia, Australia itself became the target of air and sea attacks, including a submarine entering Sydney Harbour.
Industry and society mobilised for a total defence effort. Australia's existing arms industry was expanded, and hundreds of annexes and factories established.
The NSW Department of Main Roads worked with military authorities to construct and strengthen roads around strategic locations, so they could carry military vehicles, but also be ready for immediate demolition in case of invasion.
As well as the small tunnels to help destroy access roads, new road blocks, tank traps, gun emplacements and runways were all built or planned in 1942.
In Sutherland Shire, beaches were also protected by barbed wire, street signs and names were removed, land mines laid, boats were taken off the water so they couldn't be used by advancing attackers, and the National Park was used as training ground by local troops, including the 45th Battalion.
Evidence of military presence is seen in some other places in the area, including on the southern headland of Wattamolla where there is extensive erosion due to guns and traffic on the sand dunes and a camp site is apparent at Loftus Heights.
However there are few signs remaining of the extensive military manoeuvres from 77 years ago.
Allied victories in the second half of 1942, in the Coral Sea, around Midway Island, at Milne Bay, at Guadalcanal and on the Kokoda Trail, halted the advance of Japanese forces in the South-West Pacific Area.
