The "WaWe 10" water cannon from Austria weighs 33 tonnes and is made of steel, but it failed to stand up to tests by Thuringia Police.
To put their new purchase through its paces officers pretended to be rioters and threw tennis balls, plastic bottles and eggs at the vehicles, rather than bricks, stones, bottles and Molotov cocktails as might be expected during an actual riot.
According to broadcaster MDR the tennis balls and eggs caused dents the size of fists in the armoured glass of the €900,000 vehicles.
A police spokesman told MDR that they were not expecting such widespread damage.
A report has been sent to Germany’s interior ministry which has asked manufacturer Rosenbauer for an explanation. The government has ordered 78 of the water cannons.
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