155mm
155mm is a shell or ammunition calibre.
Overview
Common type of artillery calibre.
In detail
155mm is a shell or ammunition calibre.
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
“155 mm caliber”, English Wikipedia, consulted as further reading
Consult the sourcereference work · Reputable secondary · Wikidata
Wikidata, structured authority record Q18737097: 155mm
Consult the source