Sir Michael Fallon's defence of Britain's nuclear deterrent comes as he hosts NATO's Secretary General at the nuclear submarine base in Scotland.
The two were joined by NATO's ambassadors from the 29 members to mark the 350th patrol by a Royal Navy ballistic nuclear submarine.
Standing in front of HMS Vengeance, both men reaffirmed that NATO is a nuclear alliance and committed to collective defence.
"We operate the all for one, one for all principle," Jens Stoltenberg told me.
This means that when North Korea threatens America, it threatens the whole of NATO, raising the prospect that Royal Navy submarines could be used to defend America in the event of an attack.
The Royal Navy has four nuclear deterrent submarines - one is always at sea every day of the year, its whereabouts a close secret.
Only three NATO members have a nuclear deterrent: France, the UK and US.
Britain has used this position to remind Europe that it will still be a major player in the continent's defence post-Brexit.
The Defence Secretary's article for Sky News comes days after Labour leader Jeremy Corbyn said that Britain should sign a new treaty supporting the prohibition of nuclear weapons.
Sir Michael dismissed this, arguing it is unrealistic and would make the world a more dangerous place.
Labour did not comment on Mr Corbyn's position, but gave this statement to Sky News: "Labour supports the renewal of the Trident nuclear deterrent.
"As a nuclear-armed power, our country has a responsibility to fulfil our obligations under the Nuclear Non-Proliferation Treaty.
"Labour will lead multilateral efforts with international partners and the UN to create a nuclear-free world."
Far from taking steps to scrap the nuclear deterrent, the UK is building four new ballistic submarines - the Dreadnought class - which will be ready by the early 2030s.
Some £1.3bn has also been earmarked to upgrade the Clyde base on the west coast of Scotland.
Although the deterrent is still controversial for some, North Korea has reinforced NATO's commitment to it and made it more relevant than it has been for many years.