In the late 1970s and '80s New Zealand was caught in the grip of anti-nuclear fever – nuclear-powered warships the USS Truxtun and the USS Long Beach drew protests when they visited in 1976, and there were anti-nuclear rallies in Auckland when the USS Texas visited.

Elected in July 1984 the Lange Labour Government, partly picking up on the mood of some of the population but mostly manoeurved by the 'left' of the party, made it clear that it would establish New Zealand as nuclear-free. this proved popular with 40 towns and boroughs declaring themselves nuclear-free. Lange also announced its decision to ban nuclear-powered and/or armed ships – a stand that was soon put to the test.

In late 1984 the US Government asked that the guided missile destroyer USS Buchanan be allowed to visit New Zealand. The US hoped that the New Zealand public would not realise the older ship was nuclear-armed, allowing it to slip under the political radar. Hoping the US would offer to send something less ambiguous, Lange replied that the ship's arrival "would be seen as a surrender by the Government." He hoped in vain, however: it was the Buchanan or nothing.

On February 4 1985, the Lange Labour Government refused permission for the USS Buchanan to visit New Zealand – within just days the US severed visible intelligence and military ties with New Zealand, and downgraded political and diplomatic exchanges. And, while the ANZUS structure remained in place, US Secretary of State George Schultz confirmed that the US was no longer willing to maintain its security guarantee to New Zealand.