The recoil-less [this is how the spellchecker tells me to write it] gun in question was a soviet setup invented by Kurchevsky.
Kurchevsky was a real-world mad scientist in service of the Soviet Army, whose main idea was to arm everything with recoilless automatic guns. Sadly he a)was unable to figure out a reliable feed mechanism and b) had competing recoil-less gun inventors dealt with (such as Kondakov, who had developed a reliable 75mm automatic recoilless gun). As such, after he was , in turn, executed by Stalin, the Soviet Union soured on recoil-less guns for decades to come, axing many very promising developments in the field.
Kurchevsky - being completely insane - worked on rearming the entire Soviet Army with recoilless guns, down to 12-inch naval cannon (which were actually successful in testing, but aborted with the execution of Kurchevsky. Suffice to say here that a 12-inch gun was mounted and tested on a light destroyer, and plans were already being made for a dual 12-inch system.)
In the air, Kurchevsky was working on 75mm air-to-air guns (to be used on enemy bombers), and 100mm ground attack guns. Here's an image of the latter:
Finally, a 152mm air-to-ground gun was still on the drawing board when Kurchevsky was executed.
