Bofors twin 57 mm
Bofors twin 57 mm is an autocannon or anti-aircraft gun.
Overview
Naval Gun.
In detail
It is associated with Sweden.
Sources
Each source is named with the standing the house places on it, so the evidence can be weighed rather than taken on trust.
reference work · Reputable secondary · Wikipedia
“Bofors 57 mm Naval Automatic Gun L/60”, English Wikipedia, consulted as further reading
Consult the sourcereference work · Reputable secondary · Wikidata
Wikidata, structured authority record Q10397341: Bofors twin 57 mm
Consult the source