This photo, taken at a German Army artillery range, is not a fake.

The side expansion chambers will be to accommodate the blast of the cannon’s muzzle brake.

I know what you are thinking: “WTF!”.It was build to reduce noise to communities nearby. The vehicle pictured is the M109G 155mm self-propelled howitzer.

Many thanks to Sven for emailing it to me.

UPDATE: Thanks to Mark for these images of another German tank suppressor.

UPDATE: Daniel found a US patent that German defense firm Rheinmetall GmbH has on the design of cannon silencers.