The 4" L/50 gun was the standard WW-1 destroyer gun. U.S. destroyers initially, like those of other countries, employed short-range torpedos against slow-firing enemy battleships, whose decks they could rake with comparatively small-caliber guns: 57mm and 76mm being among the most significant. However, with the ever increasing range of torpedos, the range of the defending and supporting artillery had to be increased as well. In battleships, 5" L/51 guns were mounted, but these were too unhandy and heavy to be installed in the U.S. destroyers. The 102mm gun was a perfect compromise between flat trajectory -- desirable because of the much greater chance of hitting something -- and rate of fire. Possible other weapons included the 76mm L/50, and the 127mm L/25, both of which would have higher trajectories at a given range.

    The 102mm L/40 was mounted in the destroyers of the Clemson and Wickes classes, among other ships. They were retained well into WW2 and though replaced on many of the destroyer conversions by 76mm guns (which could take on aerial targets), many of them were retained in different ships such as unmodified destroyers, transports and auxilliaries, patrol boats and most importantly, submarines. Many of the modern U.S. submarine designs were then only armed with a 76mm gun, which no submariner could find adequate. They were often replaced in service by 102mm guns, and even 127mm L/25 and L/51 guns.