Attacks on military and defence targets are not new, although previous acts of sabotage linked to Russia include more puzzling targets – such as an Ikea store and a Polish paint store.

The novelty now is the concentration of cases.

“The intensity of military sites being attacked we’ve seen over the past couple of weeks is unusual,” Daniela Richterova of the Department of War Studies at King’s College says.

She links the spike to developments in Russia’s invasion of Ukraine.

“We’ve basically seen Ukraine take the war to Russia and strike deep inside Russian territory…They [Moscow] are under pressure, they have to do something.”

Whilst some sabotage is staged to sow chaos or fear, Richterova believes the Kremlin’s aim right now is “coercive signalling”: pressuring countries to stop supporting Kyiv by raising the stakes.

After a slow start, Germany is Ukraine’s biggest supplier of military aid.

There are other theories.

To some, Russia is less concerned about “turning off the taps” of supplies to Ukraine and more about testing Nato for weaknesses.

“Russia is probing the boundaries of what’s acceptable and collecting information on the results. They find out what works, and what’s vulnerable,” argues Keir Giles from the Chatham House think tank.

He sees the sabotage campaign as preparation for the “next phase”, as he puts it, of Russia’s aggression in Europe.

“They’re assessing the willingness of the victim country to actually do something about it.”

The International Institute for Strategic Studies (IISS), which tracks sabotage cases, points to a previous surge in 2024 when Ukraine’s allies began allowing it to use Western-supplied weapons deeper inside Russia.

2024 was the year of the parcel bomb plot, when Russia was accused of sending packages containing liquid explosive to the UK and Poland.

One ignited shortly before it was loaded on to a DHL cargo plane. It is thought this was a test run for something significantly bigger.