Explanation: In WW1, the Kingdom of Italy introduced an infantry-portable automatic weapon known as the Villar Perosa, consisting of two light automatic firearms literally combined into one. Twice the barrels, twice the firepower? At this early and experimental point in portable automatic weapons, the Villar Perosa was surprisingly effective in its role as what-we-would-recognize-as a submachinegun.

The opposing Austro-Hungarian Empire realized it needed a response to this weapon, so created the Sturmpistole, which was… two fully-automatic pistols slapped together. It was not as effective as the Villar Perosa, so generally Austro-Hungarian forces preferred to use captured Italian submachineguns instead of their own, lmao.