Why Moscow could go nuclear in Ukraine war

As the war in Ukraine is about to head into its sixth month, the ferocity with which it is fought shows no signs of abating – neither on the battlefield, nor in the rhetoric emerging from Moscow and Kyiv. Russian attacks continue to target Ukrainian cities such as Vinnytsia in western Ukraine that are far away from the front lines and those like Mykolaiv and Odessa that are of high strategic value in the battle over control of Ukraine's Black Sea coast.

Meanwhile, the battle over Donbas has further intensified. Russia is currently regrouping its forces to capture the remainder of Ukrainian-held territory in the Donetsk region. While Russia has steadily gained ground in the east, Ukraine launched a counter-offensive in May to regain control of the southern region of Kherson which is critical to Russia securing a land corridor to Crimea. Having re-captured more than 40 villages since the start of the campaign, Ukraine appears to now have some momentum on this frontline.

'Judgement Day'

Buoyed by advanced western weapons systems, especially the US-supplied Himars, Kyiv has been able to target Russian command posts, storage depots, and supply lines at greater distance and with higher precision. The prospect of deploying Himars to support the counter offensive in Kherson prompted former Russia President Dmitry Medvedev to threaten "Judgement Day" should Ukraine strike targets in Crimea. The peninsula, home to Russia's Black Sea fleet, was annexed by Moscow back in 2014 and has been extremely important in Russia's war effort since February, especially as a launchpad for ground operations in the east, including the siege of Mariupol.

More recently, the Kremlin has also used Crimea as a hub for the export of stolen Ukrainian grain. Russia has repeatedly threatened doomsday scenarios of this kind. These were usually aimed at Nato, initially at weapons and ammunitions supplies, then at troop deployments. Now Moscow seems to have accepted that they can do little about arms deliveries and are repositioning on how these arms are used by Ukraine. While one could argue that the west has crossed several Russian red lines before without any consequences, Medvedev's most recent temper tantrum should not be dismissed so quickly. His use of the phrase "systemic threat" in relation to any attacks on Crimea points to one of the triggers for the use of nuclear weapons in Russia's military doctrine.

According to Russian media, Medvedev, now deputy chairman of the Russian Security Council, used a speech to military veterans in the southern Russian city of Volgograd to promise "a doomsday, very quick and tough, immediately" if Ukrainian forces were to attack Crimea. While no other state has recognised Russia's annexation of Crimea, Medvedev framed such a response as legitimate reaction to an attack on Russian territory. This narrative of defending "mother Russia" disguises how strategically important Crimea is for Russia and how dependent Moscow remains on secure staging areas and supply lines there if they want to ever advance further west on the Black Sea coast towards Odesa.

Increased attacks on Mykolaiv would suggest that this is still a possibility contemplated by the Kremlin in line with "stage-two" goals of the so-called special military operation in Ukraine, which include the complete "liberation" of Donbas and a land corridor from there along the Black Sea coast all the way to Ukraine's border with Moldova. With reference to Crimea, Moscow is now setting up another red line —- not for the west, but for Ukraine. And this creates a different, and potentially more dangerous, situation.

Autumn showdown

Part of this bigger picture is an expectation, on both sides, of a showdown in the autumn. Ukraine and Russia are both hoping to "freeze" the front lines in a favourable position before the resumption of any peace talks – likely to occur in the autumn – and before winter will make fighting more difficult. For that to happen, both sides need to mobilise more forces and replenish their equipment. While Ukraine is closer to a general mobilisation, Russia has so far avoided this and used volunteers and contractors, like the Wagner group to compensate for its manpower shortages.

Russia may have a much larger population – around 140 million compared to Ukraine's 40 million – but lacks the kind of sophisticated military equipment that Ukraine has access to. Instead Russia is increasingly relying on Soviet-era tanks and artillery. These may not have the same effectiveness as what Nato can supply, but their sheer number and ruthless use – including against civilian targets – could still overwhelm Ukrainian defenders. The long-term prospects are not encouraging for either side. A protracted stalemate in Donbas is all but inevitable once Russia has conquered the remainder of Donetsk region. When this happens it will have been at a very high cost to both sides and the civilians caught in the middle.

In the north, Russia may make a new push to re-capture Kharkiv, while Ukraine may make further advances in its counter-offensive in Kherson. None of this will constitute the significant boost to morale that both sides need ahead of any major battle in the autumn. This may increase the temptation for Ukraine to strike Russia's bridge across the Kerch Stait to Crimea and for Russia to retaliate with tactical nuclear weapons. Because it would not constitute a direct attack on a Nato member but keep the war in Ukraine, Putin may have fewer qualms carrying out this threat. Anyone relying on the Russian president's "rationality" not to be capable of such a move only needs to look back at Russia actions in Ukraine over the past eight years to realise that this is not a safe bet.

(The authors are with University of Birmingham and National University, Odesa Law Academy respectively.Courtesy: Conversation)