The last remnant of the anti-nuclear standoff has been swept aside, with approval granted for a visit by a United States warship to a New Zealand port.

Prime Minister John Key announced the destroyer USS Sampson will take part in the navy's 75th anniversary.celebrations in November.

It will be the first US warship to dock here since the ANZUS bust up over New Zealand's anti-nuclear legislation in the mid-1980s.

RNZ US ambassador Mark Gilbert tells Kim Hill that the New Zealand visit of US navy destroyer the USS Sampson next month marks a significant milestone in an improving relationship between the former Anzus partners.

"I am 100 per cent confident it meets New Zealand's law and that means it's neither nuclear powered nor carries nuclear weapons," Key said.

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And this time around peace protesters from the mid-1980s are far more relaxed about the visit.

John Anthony United States Vice President Joe Biden and Prime Minister John Key announced earlier this year that a US Navy vessel will visit for the New Zealand navy's 75th anniversary celebrations in November.

​Kevin Hackwell, who with a friend was arrested in Wellington harbour after swimming out to "tag" the USS Texas in 1983, said it was "a victory for New Zealand's anti-nuclear policy".

He would not be swimming out to protest against this visit.

"There's no ambiguity about these ships these days."

There had been doubt in the 1980s when the catchphrase was "if in doubt keep them out", but now there was no need for the US to confirm or deny if they were nuclear armed or powered.

However, there remained a bigger question about New Zealand's close links with US military strategy, and the US still had nuclear weapons, Hackwell said.

Back in 1983 - the last time a US warship visited - his plan was to spray paint a fluorescent "ban the bomb" sign on the side of the ship. But it was abandoned when the spray can's nozzle fell off. So instead a ribbon of wetsuit material was tied to its anchor chain to prove the protesters had been there.

Hackwell, who now works for conservationists Forest and Bird, said he and his mate were arrested back on shore and charged with interfering with a ship. But the charges were dropped for lack of evidence after the two US sailors who were witnesses were flown back to meet their ship in Australia.

But they did have the pleasure of delaying an on-board lunch for then-prime minister Robert Muldoon while the ship was checked.

The Sampson is a guided missile destroyer which starred in the 2012 military science fiction film Battleship. ​

​Key, who by law must be satisfied it is not nuclear powered or armed, said the process for considering the visit was the same as for all other ships attending the naval celebrations, and all military ship visits since the anti-nuclear law was enacted.

"As you would expect I went through a thorough formal process that included receiving advice from Foreign Affairs, from the Department of Prime Minister and Cabinet, the Attorney-General and from the Minister of Foreign Affairs.

"On the back of that advice I feel quite comfortable signing the declaration, which gives the approval for the ship to come."

Vice President Joe Biden in Auckland earlier this year confirmed the US Government would accept the invitation to join other nations in New Zealand to celebrate the navy's birthday, but he did not name a ship at the time.

US ambassador to Wellington Mark Gilbert said most of the ships visiting would be flagships of their countries and the US wanted to pick a ship it thought was a good example of the US navy.

"We believe the people will be welcoming of the ship to come. Almost everyone we talked to seems to be very excited about us being here."

He reaffirmed the US policy that it would neither confirm nor deny a ship's nuclear status.

Asked it he expected protests, he said: "This is a wonderful occasion for the NZ navy, and we hope everyone treats it that way."