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