The German Interior Ministry has asked for an explanation from a water cannon manufacturer, after the weapon was reportedly damaged by an arsenal of eggs and tennis balls – launched by police themselves.
Officers from Thuringia Police in central Germany posed as protesters to test the “WaWe 10” water cannon from Austria which is worth €900,000 (£246,156).
But the armoured glass of the 33-tonne steel machine was left with dents the size of fists after the team pelted it with tennis balls, plastic bottles, and eggs, according to broadcaster MDR.
Manufacturer Rosenbaurer has since been asked for an explanation after the Government ordered 78 of the vehicles with the intention of using them to dispel rioters.
The news follows efforts by London Mayor Boris Johnson to allow the use of water cannon in the capital.
The vehicles have so far only been used by UK police officers in Northern Ireland, where they were introduced to quell public disorder during the Troubles.
Those against the machines cite an incident in Germany which left protester Dietrich Wagner blinded, after he was hit by a jet of water.