This devise was allegedly built in Stuttgart and was designed to fire a blast of highly pressured air and water vapour. Early experiments showed some promise with its effective range being about 200m.
"Experimental trials of the cannon at Hillersleben demonstrated that a 25mm-thick wooden board could be broken at a distance of 200m. Nitrogen peroxide was deployed in some of the experiments so that the brown color would allow the path and destination of the otherwise transparent projectile to be observed and photographed. The tests proved that a powerful region of compressed and high-velocity air could be deployed with sufficient force to inflict some damage.
I've since seen this picture on several other sites but they all repeat the same text (copied word for word but not credited to a source I might add) so its hard to tell if this is a genuine weapon or an Internet myth that has been copied and propagated (which of course is exactly what I'm doing!). The Nazis seemed to waste a lot of time and resources on their wonder weapons, many of which never came to fruition, so a wind cannon might not be all that improbable after all. Myth or not its intriguing.