In the modern world, nuclear weapons are seen almost entirely as deterrents, with most nations adopting a “second strike” approach to even newly developed nuclear delivery vehicles like intercontinental ballistic missiles (ICBMs). This “second strike” mindset is, at its base level, an extension of the long-standing doctrine of mutually assured destruction — with nuclear nations working to ensure they can respond in kind to even the most widespread of nuclear attacks. However, the Pentagon believes that Russia, in particular, has a strategy aimed at operating just beneath the threshold of global nuclear war.

The United States seems to be looking to respond in kind.

In a recent interview with Seapower magazine, Undersecretary of Defense for Policy John Rood explained intelligence reports of a Russian plan to use low-yield nuclear weapons in the early stages of a large scale conflict with the intent of intimidating an adversary into submission. The concept would involve using small nukes, which would be deployed in a low profile manner, serving simultaneously as an effective tactical weapon and a looming threat of nuclear escalation. Currently, the United States and its allies employ only relatively large scale nuclear weapons delivered via traditional means. A small nuclear attack would force the U.S. to choose between escalating a nuclear conflict toward mutually assured destruction by initiating a full scale launch… or not responding at all out of fear of the same.

This possibility is of particular import in places like the Baltics, where Russia could feasibly cut the Baltic states off from NATO support entirely simply by capturing the narrow stretch of territory between Belarus and Kaliningrad known as the Suwalki Gap. Once the gap falls, Russia could rapidly take over Latvia, Estonia, and Lithuania — then use low-yield tactical nukes near Poland’s borders to show that Russia is willing to use its nuclear arsenal to defend its newly acquired territory.

The Suwalki Gap (As shown by Google Maps)

In order to mitigate this possibility, Rood continued, the U.S. military needs to develop low-yield nuclear weapons to match Russia’s capabilities. These weapons likely would not be deployed in the same ways as America’s current nuclear arsenal is. While a smaller warhead could simply be mounted on existing submarine-launched missiles, for instance, there would be no way for the Russian military to assess the yield of the weapon while it would be en route — potentially prompting them to respond with a full scale launch of their own.

Instead, novel deployment strategies would have to be employed to ensure that Russia (or potentially China) couldn’t mistake these low-yield nukes for their bigger siblings.

The concept of low-yield nukes isn’t a new one. In fact, during the Cold War, there was one U.S. Special Operations unit tasked specifically with the delivery of “backpack nukes” called Special Atomic Demolition Munitions, or SADMs. The U.S. government designed a variety of these man-portable nuclear weapons with destructive yields that ranged from 100 tons of TNT to 1,000 (.1 to 1 kiloton). They weighed approximately 59 pounds and were always meant to be delivered via a two-man team.

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Although the deployment of the weapon could really be handled by just one special operator (these weapons never reached the conventional forces), nuclear doctrine dictated that no single person — other than the president — ever have the means to detonate a nuclear weapon on their own. As a result, each special operator was given one half of the detonation code; both would need to input said codes in order to start the countdown on the weapon.

The very premise of using low-yield nuclear weapons to deter the use of larger nuclear weapons may sound a bit shaky: But Russia has already demonstrated a propensity to operate within the “grey zone” — just beneath overt acts of war — when it comes to cyber and even kinetic attacks. It stands to reason that Russia’s success in these “grey zone” operations could eventually embolden it to create a nuclear grey zone by using a similar rationale and leveraging NATO’s reluctance to go to war.

Russia is aware that NATO doesn’t want war. Because of that, Russia is able to push small boundaries that it knows aren’t in themselves significant enough to warrant a global conflict.

Likewise, Russia knows that NATO really doesn’t want nuclear war. So in the event that Russia ever felt truly threatened, it could resort to using low-yield nuclear weapons as a way of reminding the world that poking the Russian bear may result in the end of civilization.

In such a case, some Defense officials believe that responding in kind would show the Russians that America is prepared to meet them at that level… but the chances that such a confrontation would prevent nuclear escalation from there is up for debate.