A historical note: the 3-inch guns were used by towed tank destroyer units, and were not issued as infantry AT guns. The towed TDs were adopted as an economy measure to be used to support the infantry divisions, but they didn't work out as well as the SP tank destroyers. The US M5/M6 guns were rather heavy and in the Ardennes hey showed that they couldn't keep up with mobile attacks. By the end of the war in Europe, most towed TD battalions had been converted to self-propelled. The standard towing vehicle for the 3-inch AT gun was he M3A1 halftrack.
Funny enough, there are several 3-inch guns still in active service in the US Army! They are used as salute guns by the 3rd Infantry in Washington, DC.
Gary B.
Waverly, NE