Since February’s invasion of Ukraine, Russian forces have suffered setback after setback on the battlefield, leaving President Vladimir Putin fewer choices if Russia wants to extract itself from what increasingly looks like defeat.

Every major Russian setback triggers heated global discussion on whether Putin will resort to using tactical nuclear weapons in order to reverse the course of the war and re-establish Russia as a great power rather than a humiliated giant.

What are these weapons and what are the likely scenarios in which they could be used? 

What they are:

Tactical nuclear warheads were created to give military commanders more flexibility on the battlefield. In the mid-1950s, as more powerful thermonuclear bombs were being built and tested, military planners thought that smaller weapons with a shorter range would be more useful in “tactical” or military situations.

Modern warheads have a variable “dial-up” yield, meaning an operator can specify its explosive power, and a tactical weapon could be anywhere from a fraction of a kiloton to 50kt in strength.

A single kiloton is equivalent in power to a thousand tons of high-explosive TNT.

For a sense of destructive scale, the weapon that destroyed Hiroshima was roughly 15kt.

Nuclear weapons possess several deadly aspects to them.

The heat from the blast can be hotter than the surface of the sun, the immense power released by the weapon producing an incredibly powerful blast wave that destroys everything in its path outward to several kilometres.

On detonation the intense radiation burst will kill anything living nearby and the resulting radioactive fallout poisons the ground for tens of kilometres from the blast zone, forming a deadly shroud that can kill weeks and even months later.

A single tactical nuclear weapon could destroy an airfield, a port, concentrations of troops and tanks or supply depots. They can be delivered by aircraft, ballistic and cruise missiles; some can even be fired from artillery.

Despite being a possible temptation to use by military leaders, no country has yet broken the seven-decade taboo on the use of nuclear weapons since the destruction of Nagasaki in 1945.

While nuclear weapon stockpiles are much lower than during the Cold War, they are still large enough to be able to destroy most of humanity in a few hours.

Battlefield nuclear weapons are only the trigger for what most analysts and politicians fear would be a quick and uncontrolled escalation to strategic nuclear weapon use and the destruction of civilisation being the inevitable result of such a conflict.

The inherent danger in the use of even a single nuclear weapon is that it would likely invite a terrible response from an opposing side in order to deter the opponent from using more.

It is the response, the attempt to firebreak a nuclear conflict before it gets started, that is also the mother of all gambles. Get it wrong and the world could die.

It is this fear that our destruction would be mutually assured (MAD – mutual assured destruction – military doctrine), that has kept militaries in check throughout the Cold War up until today.

But, if nuclear weapons are that awful why use them at all?

Russia caught between a rock and a hard place

Russia’s reputation as a great power is in tatters. Its military has been exposed as shockingly inept and methodically brutal.

Russian armed forces have suffered significant defeats. Driven from the outskirts of the capital, Kyiv, early in the invasion, Ukraine’s successful counteroffensive is now driving Russian units from the towns they had initially captured in the northeast.

Russia’s flagship Moskva – a guided missile carrier – has been sunk; Snake island was recaptured from its Russian occupiers, the Kerch Strait bridge linking Crimea and Russia was badly damaged, and now Ukrainian forces are encroaching on a pocket of Russian forces, centred around Kherson city in the south. Ukraine is squeezing it daily and shrinking its perimeter as the tens of thousands of Russians there are increasingly cut off from the likelihood of resupply.

This is Russia’s disastrous legacy in the conflict so far. President Putin has few choices left other than to admit defeat.

The call-up of 300,000 Russian reservists, a psychological shock to Russians and the first such call-up since World War II, has yet to make itself felt on the battlefields of Ukraine.

Will they be enough in themselves to turn the tide against Ukrainian troops? While the arrival of large numbers of Russian reinforcements is not insignificant, there are persistent reports of poor equipment and a lack of warm clothing.

Though battle-hardened, Ukrainian forces are also nearing exhaustion after months of constant combat.

If Putin’s latest plan fails, he can either go for mass conscription, which will likely cause civil unrest, or further denude his armies in the east of the country. Able to send tens of thousands of troops to participate in September’s Vostok military exercises during a war, the Russian president clearly still has significant resources at his disposal.

However, Ukraine has learned the harsh lessons of 21st-century warfare while Russia is still mired in the past, its poorly trained soldiers so far being no match for the Ukrainians.

It is at this juncture that nuclear weapons’ use would be the most likely, if it were to happen at all.

Three possible scenarios for Russian nuclear weapons use:

The first, and perhaps least likely, is an actual nuclear strike against an obvious military target on Ukrainian soil. It would be somewhere relatively unpopulated in an effort to minimise the spread of radiation, an air burst over an air base or a concentration of troops.

Not only would this be relatively ineffectual given the dispersed nature of Ukrainian forces, but it could likely invite an immediate and significant reprisal attack directly by the United States and NATO forces.

The dangers of escalation are all too grim and obvious.

The second scenario would be a demonstration over the Black Sea in international waters. While a massive pollutant and still risky, it would not be the obvious trigger for a NATO response and potential escalation could still be stopped at that level.

The third, and perhaps most likely use of any Russian nuclear weapon would be to conduct a test on Russian soil, on one of the old Soviet nuclear test sites in the north, like Novaya Zemlya. Though breaking the Test Ban Treaty on atmospheric testing, it would be unlikely to invite a military response from NATO.

Such a test would remind the world that Russia has other means at its disposal in the form of terrifying weapons, that its humiliation will only go so far, and it is resolved to use them if Russia is not allowed to extricate itself from this conflict with something that does not look like total defeat – a 50kt bargaining chip, with megatonnes in reserve.

Whichever scenario is played out, the detonation of a nuclear weapon would likely trigger panic around the world followed by civil disorder as cities empty. There would also be chaos on global stock markets as currencies and stocks plunge in value.

What is the likelihood that such a weapon would be used?

While still low, for the first time in decades the probability that nuclear weapons could be used is not zero.

No one has anything to gain from nuclear conflagration.

But an embattled Putin may feel he is being forced to make a desperate gamble.

His high-risk use of one of the few tools left available to him could help stop a war, his war, from ending in total defeat for Russia, allowing its forces to leave the battlefield beaten but not completely broken.