A specialist dive team has begun a complex operation to remove a suspected unexploded bomb that could have sat on the sea floor of Darwin Harbour for up to 80 years.
The Royal Australian Navy's Clearance Diving Team One was deployed to Darwin on Friday to retrieve the item, suspected to be an old mortar shell, discovered during a survey of the planned site of the Darwin Ship Lift project this week.
On Saturday, a Defence spokesman said a team of five divers were using sonar equipment to search for the "unexploded ordnance" after failing to locate it on Friday.
The team has been involved in operations in Vietnam, Kuwait, East Timor and across the Middle East since being established in 1966 and were deployed to Darwin following the suspected ordnance.
A Department of Planning, Infrastructure and Logistics (DIPL) spokeswoman told the ABC earlier this week that the object appeared to be a mortar shell, though that had not yet been confirmed.
She said the object, which measured between 60 and 80 centimetres long, had been found resting on the ocean floor.
A relic of Darwin's wartime past
Darwin was one of a number of locations across Northern Australia that were bombed by Japanese forces during World War II, as part of strategy to prevent the Allies from having an air base in the country.
The Northern Territory capital was the major target of those raids, with the bombing of Darwin on February 19, 1942 still the largest and deadliest single attack ever mounted by a foreign power on Australian soil.
Military historian Tom Lewis said a range of bombs had been left behind in the 208 raids on Northern Australia, from mortar shells fired by the army to larger bombs dropped by planes.
"Of the bombs released, sometimes the bombs don't go off. That's fairly normal for World War II or indeed today – you get a certain percentage that just don't detonate, for one reason or the other," he said.
"Years later somebody finds them, and then you've got a problem.
"You've got this container full of explosive with a detonating system, and possibly it's going to go off.
Dr Lewis said ammunition from the war could still be found in parts of Darwin, especially on the city's beaches.
However, he said discoveries were becoming rarer over time.
"It's been the case that the Northern Territory, after the troops left and the civilians came back in the 1950s, this was common across Darwin suburbs, and it's become less common over the years as they've been found," he said.
"But still, there's a lot of the Northern Territory that has yet to be really explored or developed, so you're going to find them for some decades to come."
Even before the suspected ordnance was found on Monday, divers had also found spent rifle cartridges and multiple rounds of bullets at the survey site.
Fishers warned to take care
A 250m-wide exclusion zone was set up around the object earlier this week, with harbour users warned to steer clear.
The zone has been marked out by yellow buoys that will be illuminated by lights at night, and warning signage will be erected at several nearby boat ramps in coming days.
The zone falls within an area used by commercial shipping operators – though the channel remains open – as well as recreational fishers trawling for barramundi.
Amateur Fishermen's Association of the Northern Territory (AFANT) chief executive David Ciaravolo urged recreational fishers to make themselves aware of the zone and stay clear.
"I think, in conjunction with the notices out on social media, the notices to mariners and the notices at the boat ramps, there should be a good level of awareness," he said.
Compliance with the exclusion zone has been good so far, according to DIPL, who thanked the public for their adherence.
A spokeswoman said any harbour users who failed to heed the zone could be issued with a fine.
