The 1.1-inch weapon was too heavy for a true last-ditch mount yet too light to bridge the gap to five-inch guns. Its unresolved faults left the US Navy with a critical short-range anti-aircraft weakness by 1940, but Pearl Harbor forced ships to fit whatever weapons were available. Twenty-millimetre Oerlikons could be installed widely in single or twin mounts and supplied an urgently needed close-range layer. Swedish development of the Bofors sought more range and accuracy from two-pounder pom-pom concepts, while Oerlikon's development likewise improved an existing weapon. The longer-ranged 40 mm Bofors became the more capable intermediate gun fleets had been seeking between machine guns and heavy dual-purpose artillery.
Chapter · 24:28-28:24
The wartime short-range anti-aircraft gap
The US Navy moved from the unsatisfactory 1.1-inch gun through mass Oerlikon fittings to the more capable 40 mm Bofors.