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Any more context on this image? My understanding is that AA guns are shockingly inefficient, and I'd expect a tank gun to be almost useless unless it's a specific tactical scenario.
I imagine it was most used against close air support, not high-altitude bombing. Seeing what to bomb in the dense woods would require flying pretty low and slow, which makes you a great target for a big semi-auto gun like this.
Another good motivator is that a bigass rifle is really flexible (sort of). You can shoot at vehicles, bunkers, snipers, harass tanks, and apparently also planes.
A twin-mounted full-auto variant was kept in service till the late 70s, mostly for anti-helicopter purposes, so it's probably a pretty decent piece of kit.
It probably was almost useless, but in WW2, such ad-hoc anti-aircraft measures were still attempted against dive bombers and the like.