One of the United States' most senior retired military officers has warned during a visit to Australia that North Korea will not wind back its nuclear program and will need to be strongly deterred, including possibly through nuclear weapons positioned in Asia.
"I am not optimistic that we're going to be able to take the existing goals that we've had for the peninsula and move to a denuclearised state," Patrick Walsh, a retired four-star admiral who commanded US naval forces in the Pacific, told Fairfax Media in an interview.
"I think the prevailing view will be that North Korea is now a nuclear state and it will require a much stronger deterrence posture on the part of allies in the region," he said.
"They may be the first to nuclearise in the region but I don't think they'll be the last."
In a frank assessment, Mr Walsh, who as head of the Pacific Fleet commanded 180 ships and more than 125,000 personnel and has also served as vice-chief of naval operations, warned that strong deterrence would carry the risk of miscalculation leading to conflict because the closed-off regime of Kim Jong-un could not be trusted to interpret correctly moves by the US and its allies.
Therefore as countries such as Japan and South Korea inevitably strengthened their defence postures, Mr Walsh said it was vital the neighbourhood was "very clear and very credible and transmit[s] in very unambiguous terms to North Korea what the posture is - so there's no surprise".
Mr Walsh described stronger deterrence as a situation in which "there's more muscle, it's more transparent, it's really clear as far as the communication is concerned".
He said when Washington talked about all options being on the table, tactical nuclear weapons - which are intended to be used in a conflict as distinct from so-called strategic weapons, which are held over an enemy as a perpetual threat - were "probably part of the conversation". He said such a drastic move would show "we're serious about this".
US Secretary of Defence James Mattis confirmed on Tuesday that he had discussed with South Korea positioning US tactical nuclear weapons in the South.
Mr Walsh, now a vice-president with global cybersecurity firm FireEye, is visiting Canberra this week to take part in an Australian government cyber war games, which are testing the information security capabilities of a range of government departments.
He said cyber would likely play a significant role in the future encounters between North Korea and the US and its allies.
Illustrating the fraught situation the US and its allies are in, Mr Walsh said stronger deterrence would likely be seen by Pyongyang as "escalatory" and therefore prone to miscalculation on Mr Kim's part.
"They'll be rational steps through a western lens but, through the North Korean lens, I can imagine their reaction if Japan or the US shot down one of those missiles ... It's ripe for miscalculation."
Asked whether the US and its allies by tacitly acknowledging North Korea as a nuclear state risked accepting it as a strategic equal and giving it too much clout, he said "there was a time and place where everyone avoided that".
But he added: "I think we're beyond that. I think the longer we assume they don't have nuclear capability, the longer we prolong reality of trying to deal with them as a nuclear state. They are not going to denuclearise. So if they're not going to denuclearise, then what are you going to do next is really the question for our national leaders."
Mr Walsh also backed calls for China to do more, saying in Beijing there was a "realisation that the path they have traditionally taken when it comes to their relationship with North Korea has brought us to where we are and it's not a good outcome".