The navy has neutralised a set of World War II-era mines found on the seafloor in the Hauraki Gulf near Auckand.
According to the New Zealand Defence Force, the mines were laid during the early parts of the war to protect Waitematā Harbour and the Hauraki Gulf from threats posed by the Japanese and German navies. They were designed to be detonated from stations on the shore if the enemy was spotted.
By 1944, the Allies were pressing on Berlin and pushing Japan’s advances back, meaning the threat of attack had reduced. The mines were decommissioned by remote detonation.
But, in the channel between Whangaparāoa Peninsula and Tiritiri Matangi Island, some mines misfired.
“It is believed that during the subsequent clearance by minesweepers, some mines became dislodged from their moorings and, over time, corroded and sank to the seafloor where they drifted with the currents,” the NZDF said.
In 2014, a Royal New Zealand Navy Maritime Explosive Ordnance Disposal team found and disabled some mines.
In March this year, a further five were found in the area, at a depth of between 21 and 28 metres.
Over three days this week, navy divers got to work disabling the historical explosives. Marine mammal observers monitored the operation for the presence of whales, dolphins, and other protected species.
Divers used low-level explosive charges to crack the mine casings, allowing seawater to disarm the mines permanently.
“These carefully calibrated charges are designed to minimise environmental impact and disturbance to marine life,” the Defence Force said.
“The controlled explosions, which effectively defused the mines, were barely audible and created no visible disturbance on the surface.
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Officer in charge of the disposal team, Lieutenant Warwick Creasy, said the work was dangerous but it was routine for the navy in the Pacific islands, where unexploded mines remained an issue.
“But these mines are very close to home, so we wanted to take every precaution to ensure they no longer posed a threat to commercial and recreational fishers, divers, or the marine environment.
“The task went exactly according to plan which reflects the intensive training we undertake, careful preparation and the type of extreme care that goes with the handling and placement of high explosives. Job done. Home safe.”
