"It is the closest Germans ever got to the shores of New Zealand during World War II," says Mr Shone.
"It was a most unusual decision to go into Gisborne's harbour. The sheer audacity of a big submarine to come into a port as small as Gisborne's was very risky."
The U-boat had departed from Jakarta, then known as Batavia, in Netherlands East Indies - now Indonesia.
Its mission took it to Australian waters, where it sank a US Liberty boat offshore from Sydney on Christmas Day 1944.
With the Australian navy and air force seeking quick revenge on the submarine, Commander Heinrich Timm escaped across the ditch to New Zealand to avoid detection and find further merchant ships to destroy.
After travelling down the East Coast of New Zealand, U-862 spent the daylight hours of January 15 lying at periscope depth out from Kaiti Beach, waiting for a ship worth sinking to pass.
Because no ship left or entered the harbour that day, U-862 entered Gisborne's harbour on the surface at midnight to see whether any sizable ships were berthed at the pier.
Commander Timm took the submarine into the harbour as far as the Kaiti Basin but found only small fishing vessels.
He thought briefly about the possibility of sinking the harbour dredge A.C. but decided not to because he was worried about giving away the presence of his submarine before he headed for Hawkes Bay.
The harbour dredge A.C. narrowly missed out on being sunk by the German U-boat. Photo / Supplied
After leaving Hawkes Bay empty-handed, the crew abandoned an attack on Wellington harbour when they were urgently recalled to the Far East a few days later.
Having made no attacks on New Zealand ships, the U-boat's presence in New Zealand water went undetected, and came to light only in 1992 when first watch officer Gunther Reiffenstuhl published his personal war diaries.
"It is pure luck that the first watch officer decided to make his diaries public," says Mr Shone.
"Without them, we may never have known."
Mr Shone interviewed the first watch officer in 1997, after being invited to Austria for a reunion of the submarine's crew.
"The U-boat men were quite interested in talking about what had happened during their three months travelling around Australia and New Zealand, and they were very forthcoming in giving me information," says Mr Shone.
"Their attitude was that after 52 years, they were more than happy to discuss it."
Mr Shone says the crew were extremely lucky to make it out of Gisborne harbour undetected.
"From harbour records, I discovered the submarine came into the harbour with only one metre of water under its hull.
"The captain had no idea how shallow it was. They took an enormous risk because it could easily have run aground."
Had it run aground, the crew would surely have become New Zealand's only military prisoners of war captured on home soil.
Although no celebrations are planned for the anniversary, Mr Shone says it is an event worth acknowledging.
"It's an important historical event and it is worth recalling that this happened 70 years ago, especially now only three or four of the crew are still alive."
Mr Shone has recently completed his book, titled U-boat in New Zealand Waters, and hopes to have it published this year.
- Gisborne Herald
