Social media was buzzing earlier this week with restaurant reviews from the Kursk region of Russia, written by Ukrainian troops. They were clearly enjoying the fact that after months of grinding retreat in the face of a relentless Russian advance, they now found themselves on the other side of the border.

Their lightning-fast incursion onto Russian soil had taken the Russian army by surprise. By Wednesday evening, they controlled about 1,000 square kilometres of Russian territory. One of the facetious messages read (in translation):

A group of us will be visiting in a few days and were wondering if you have parking for about a dozen tanks? Please bear in mind we have British Challenger II tanks, which are much bigger than Russian ones.

Russian border guards had reportedly raised the alarm that Ukrainian units were massing near the border. But neither the Russian commanders, nor pretty much anyone else watching the conflict closely, believed that Ukraine – under pressure along the frontline in Donbas – had the manpower to launch an operation of this kind, writes Patrick Bury, a reader in security at the University of Bath.

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Bury, who came to academia via the British army and a role as an analyst with Nato, specialises in warfare and counter-terrorism. He believes that surprise was the key to the success of the incursion, ensured by careful operational security.

It would have been an operation months in the planning, writes Bury, rapidly establishing and maintaining strong air defence and electronic warfare bubbles over their advancing troops. The effect has – so far at least – been a stunning........

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