"There's something quite confronting about this picture which captures these deadly mines bobbing in the water, with the Bay of Islands' distinctive Ninepin Rock, or Tikitiki, on the horizon," says Heritage New Zealand's Northland manager, Bill Edwards.
"It's a seascape loved by thousands of visitors – and yet here we see a bunch of mines floating in the water where many of us enjoy recreational water activities today.
''It's a stark reminder that Northland was a fortress on high alert against attack after the bombing of Pearl Harbour."
The photo was taken by Tudor Collins, who served as a petty officer in the Royal New Zealand Navy during the war.
Before this, Collins had developed a reputation as a noted freelancer who was one of the first photographers in Napier after the Hawke's Bay earthquake of 1931. He recorded Auckland's Queen St riots in 1932, and was the only photographer to meet the passengers and crew from the mined Niagra in June 1940.
He also took iconic photos of Northland's kauri industry and development.
"Despite the military purpose of Collins' photo, it's as much an example of New Zealand social history as his pre-war work," Edwards said.
The mines depicted may have been part of a network of 13 loops of 16 contact mines in the channel between Moturoa and Moturua islands, or more likely some of the 258 contact mines laid in three lines between Ninepin Rock and Whale Rock.
Further north, the Whangaroa Harbour was protected from seaborne invasion by a line of 30 mines across the entrance to the harbour which would have been activated from a Controlled Mining Station.
After Pearl Harbour, New Zealand became intensely aware of its vulnerability to Japanese attack and Northland was seen as the most likely launch point for an assault on Auckland.
This fear was heightened when British naval strength – the great hope of New Zealand defence – was severely undermined with the sinking of the Prince of Wales and the Repulse days after Pearl Harbour.
Hong Kong fell to the Japanese on Christmas Day 1941, and in February 1942 Singapore surrendered. Days later Darwin in Australia was bombed, and many feared Auckland would be next.
"In early 1942, New Zealand's susceptibility to military attack was acute. Military attention turned to Northland, and efforts were made to strengthen the region's defences," Edwards said.
"The crisis saw the Public Works Department go into overdrive. A network of military camps, mine stations, air strips, lookout posts – to name only some of the military structures – were built in strategic locations all over the region."
Not that this work was widely publicised. With information about these facilities classified as secret, and with civilian interaction strictly limited, not much was known about the overall scale of military infrastructure in Northland.
"Jack and Bill have researched what information exists about these installations and are finalising the results of their work,'' Edwards said.
"Once completed, the inventory will provide a perspective on Northland's defence network which very few people have previously had – perhaps only those at the highest levels of government and military command during the Second World War."
