When New Zealand and Australia aligned themselves with the United States via the ANZUS agreement in 1951, they effectively accepted the protection of what some described as the nuclear umbrella. Nuclear weapons played a major part in the United States' military arrangements, and the possible use of nuclear weapons or nuclear-powered vessels was implicit in any United States response to an attack on New Zealand.
While from the 1960s New Zealand consistently protested against nuclear testing in the Pacific, its defence arrangements meant that it engaged with nuclear weaponry in other forms. From the early 1970s to the mid-1980s two key issues emerged: opposition to French nuclear tests at Mururoa and to American warships' visits to New Zealand. The sinking of the Rainbow Warrior in Auckland in July 1985 was a defining moment in this period.