Yep they were called "Bordkanone" they were very effective against Soviet tanks during Kursk Hans Rudel loved 'em in fact it was him who suggested to use these on Stuka's
https://en.wikipedia.org/wiki/BK_37
To tell you the truth however, the role of ground-attack aircraft has commonly been overestimated.
http://www.operationbarbarossa.net/combat-aircraft-versus-armour-in-wwii/
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Combat footage of the 800 mm Schwerer Gustav siege gun in Crimea, 1942, taken from a Wochenschau newsreel. Starting from 1:20 Franz Liszt's Les préludes (a symphonic poem also used in other Wochenschau episodes) runs synchronously with the railway gun firing which is quite funny in my opinion