United States, 1943-1945 (500MB download, please be patient!)
The M5 3-inch AT gun was a gun looking for a branch to use it. Earlier AT guns like the 57mm M1 and the 37 mm M3 were attached the the infantry, 3 to a company, but the infantry found it too big and heavy to operate, despite its increase in performance over earlier guns, and tank destroyer branch was focused on fast self propelled guns. However, by 1943 experiences in Italy left TD branch wanting a towed gun for better concealment, and the M5 was it.
The gun itself was a combination of the barrel of a 3in M1918 AAA gun and the carriage and recoil system of the 105mm M2. The gun offered performance good enough to destroy Tiger tanks at normal combat ranges, although the tank still suffered against the Panther. It was the last conventional AT gun produced by the US, with later systems being either recoilless rifles or ATGM based.