The long-planned drill, which involves no live nuclear bombs, is routine practice for the North Atlantic Treaty Organization to ensure it is ready to use its ultimate weapon if necessary.

As tensions have risen with Russia over the war in Ukraine and repeated air incursions, it is now also an unmistakable message to Moscow of NATO's potential might.

For the first time, NATO this year allowed a small group of journalists including AFP on site during the two-week exercise.

Involving over 70 aircraft from 14 countries and some 2,000 personnel, the 2025 iteration of the drill is focused on the North Sea region.

The press invitation was part of the Western political and military alliance's shift away from a deep culture of military secrecy -- up until four years ago it didn't even divulge the name of the nuclear exercise.

"We've long not talked about this, but it's certainly time that we talked to our publics about it," said US Air Force Colonel Daniel Bunch, chief of NATO Nuclear Operations.

"This is not sabre-rattling. This is about consistently performing our mission and going out and demonstrating the full range of capabilities that the alliance has."

NATO's increased openness about its nuclear activities comes as Moscow has adjusted its own nuclear rhetoric in line with the ebbs and flows of the war in Ukraine.

Jim Stokes, NATO's Director of Nuclear Policy, insisted that the alliance's increased messaging wasn't "necessarily directed at Russia".

"It's about communicating to our domestic audiences," Stoke said.

"We want to make sure that folks understand that we're a responsible nuclear alliance, what we're doing is transparent as we can be, we are not acting aggressively."

- 'No doubt' -

But in typical NATO fashion, the transparency only went so far, given that the operation is one of the alliance's most closely guarded secrets.

Journalists watched a string of Dutch and German jets capable of carrying tactical nuclear payloads streak into the skies.

But the media was not allowed to see the crews practising prepping the dummy bombs for loading.

Such is the sensitivity around a nuclear exercise that none of the planes participating are actually carrying even the mock-up weapons.

NATO's nuclear deterrence relies on US weaponry stationed in numerous bases in Europe.

While doubts have been raised about Washington's reliability under President Donald Trump, commanders were adamant that nothing has changed.

"I don't think anybody should question the American role," said US Colonel Bunch.

Russia's recent air incursions in Poland and Estonia, and a string of unexplained drone flights, have rattled NATO.

But Marcel van Egmond, head of the Netherlands air combat command, said that security at the bases involved in the exercise was as high as ever.

"We haven't taken any specific measures," he said. "Our self-defence has been part of our mission, always."

For those involved in the exercise, the weight of training to use such devastating weapons is heavy.

"It's a strain. It's hard. It's obviously the biggest violence you can give to a pilot," said Dutch squadron commander Bram Versteeg.

But he insisted that "deterrence is all about (how) you have to be capable, you have to be credible, and you have to communicate."

"So no doubt in my mind that my people are up to the task," he said.