Will the US navy be able to visit NZ?

The MP who promoted nuclear-free legislation in the mid-1980s says it is time to welcome an American Navy ship back to New Zealand.

One may visit New Zealand waters for the first time in 30 years to help mark the 75th anniversary of the navy in November next year, if the United States accepts the invitation.

The last visit was in 1984, before New Zealand declared itself nuclear-free and its participation in the Australia, New Zealand, United States Security (ANZUS) defence alliance ended.

Former Labour minister Richard Prebble introduced bills to ban nuclear armed and powered ships, and in 1987 the government did so.

Mr Prebble said the US Government has said it had taken nuclear weapons off its ships.

A problem only arises if the ship is nuclear powered, he said.

"We know that American warships don't carry tactile nuclear weapons. Providing the ship is not nuclear-propelled I can see no reason why the prime minister cannot certify that he is satisfied the ship is not carrying nuclear weapons."

The Defence Force has invited the US navy to visit in November next year, along with the navies of 30 other countries.

But former Green MP Keith Locke said under the nuclear-free legislation the Prime Minister must be satisfied that any warship is nuclear-weapons-free.

He said the Americans would not send a ship if the Prime Minister specifically said it was not carrying nuclear weapons, as that would violate their policy of neither confirming nor denying whether its warships are carrying nuclear weapons.

The public will have to watch the wording of statements about a US Navy ship visiting as the language around the specifics could be fudged to let it in, Mr Locke said.

The Defence Force said the invitation reflected a good bilateral relationship. In late 2012, the United States lifted a ban on visits by New Zealand warships, which led to a thawing in tensions.

In 2013, HMNZS Te Mana visited the US port in Guam, the first such visit in 30 years.