Mk 12
Mk 12 is a HS.404 or autocannon.
Also recorded as Colt Mk 12; Colt's Manufacturing Company Mk 12; Colt's Manufacturing Company Mark 12; Mark 12; Colt Mk 12 cannon; Colt Mark 12.
Overview
20 mm autocannon aircraft armament.
In detail
It is associated with United States.
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
“Colt Mk 12 cannon”, English Wikipedia, consulted as further reading
Consult the sourcereference work · Reputable secondary · Wikidata
Wikidata, structured authority record Q1112061: Mk 12
Consult the source