In the Soviet Union to develop such weapons.
Here is an excerpt from an article on 45-mm guns:
"Silent," the 45-mm antitank guns
In 1935 the first samples were made 45-mm antitank guns, in which the bore after firing a special sleeve closed. The sound remained, but his strength did not exceed the power of sound when firing a revolver.
From the article it is not clear whether this is only experimental gun or was made a small lot of such guns for special operations. In any case, these guns could not be much.