"Plan A" is an audio-visual simulation that shows how so-called "tactical" nuclear weapons could lead to a highly fatal global conflict between the Russia, the US, and allies. Princeton University/Nuclear Futures Lab

A new simulation called "Plan A," by researchers at Princeton's Program on Science and Global Security, shows how the use of one so-called tactical or low-yield nuclear weapon could lead to a terrifying worldwide conflict.

In the roughly four-minute video, a Russian "nuclear warning shot" at a US-NATO coalition leads to a global nuclear war that leads to 91.5 million deaths and injuries.

Under President Trump, the US is ramping up production of tactical nuclear weapons, ostensibly to target troops and munitions supplies. While advocates say these weapons would keep wars from escalating, the simulation finds the opposite outcome.

The dissolution of the INF treaty in August raised the stakes for nuclear war, as both the US and Russia were free to develop weapons previously banned under the treaty.

On Jan. 23, 2020, the Bulletin of the Atomic Scientists moved its Doomsday clock to 100 seconds to midnight, the closest it has ever been, in a dire warning about the rising dangers of a nuclear catastrophe as Cold War-era treaties end.

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More than 91 million people in Russia, the US, and NATO-allied countries might be killed or injured within three hours following a single "nuclear warning shot," according to a terrifying new simulation.

The simulation is called "Plan A," and it's an audio-visual piece that was first posted to to YouTube on September 6. (You can watch the full video at the end of this story.) Researchers at the Science and Global Security lab at Princeton University created the animation, which shows how a battle between Russia and NATO allies that uses so-called low-yield or "tactical" nuclear weapons - which can pack a blast equivalent to those the US used to destroy Hiroshima or Nagasaki in World War II - might feasibly and quickly snowball into a global nuclear war.

"This project is motivated by the need to highlight the potentially catastrophic consequences of current US and Russian nuclear war plans. The risk of nuclear war has increased dramatically in the past two years," the project states on its website.

The video has an ominous, droning soundtrack and a digital map design straight out of the 1983 movie "WarGames." The Cold War-era movie, in which a young Matthew Broderick accidentally triggers a nuclear war, "was exactly the reference point," simulation designer Alex Wellerstein told Insider.

But while simulations can be frightening, they can also be incredibly helpful: governments can use them to develop contingency plans to respond to nuclear disasters and attacks in the least escalatory way, and they can also help ordinary citizens learn how to survive a nuclear attack.

"Plan A" comes as tensions between Russia and NATO allies ratchet up. Both Russia and the US are testing weapons previously banned under the Intermediate-range Nuclear Forces treaty, often called INF. Russian bombers have also cruised into US airspace repeatedly, and the US recently sent its B-2 Spirit stealth bomber on a mission in the Arctic - right in Russia's backyard.

This is how a NATO-Russian confrontation could quickly escalate into nuclear war.