Treaty limits raised the prospect that ships would operate without enough aircraft carriers to provide fighter protection wherever it was needed. Their guns therefore needed enough destructive power and volume of fire to kill attacking aircraft. Against lightweight aircraft of the early 1920s, a 12.7 mm hit could appear nearly as useful as a 20 or 40 mm hit at expected engagement ranges. Larger aircraft in the 1930s increased the value of a heavier shell that delivered more damage. Geography also shaped the choice: open Pacific sightlines favored the Bofors' greater reach, while islands, inlets, and other restricted approaches increased the value of immediately concentrating Pom-Pom fire. Britain retained the Pom-Pom because its existing training and production systems supported a weapon that already fitted British doctrine.
Notable Point · 36:07-43:13
Aircraft growth makes 40 mm volume of fire decisive
As aircraft became larger and tougher in the 1930s, navies needed both destructive shells and enough barrels to defeat attacks that fighters might not intercept.