Anti-aircraft warfare
Naval aspects

WWI had been a war in which air warfare blossomed, but had not matured to the point of being a real threat to naval forces. The prevailing assumption was that a few relatively small caliber naval guns could manage to keep enemy aircraft beyond a range where harm might be expected. In 1939 radio controlled target drones became available to the US Navy in quantity allowing a more realistic testing of existing anti-aircraft suites against actual flying and manoeuvring targets. The results were sobering to an unexpected degree.

The United States was still emerging from the effects of the Great Depression and funds for the military had been sparse to the degree that 50% of shells used were still powder fused. The US Navy found that a significant portion of its shells were duds or low order detonations (incomplete detonation of the explosive contained by the shell). Virtually every major country involved in combat in World War II invested in aircraft development. The cost of aircraft research and development was small and the results could be large. So rapid was the performance leaps of evolving aircraft that the British High Angle Control System (HACS) was obsolete and designing a successor very difficult for the British establishment. Electronics would prove to be an enabler for effective anti-aircraft systems and both the US and UK had a growing electronics industry.

In 1939 radio controlled drones became available to actually test existing systems in British and American service. The results were disappointing by any measure. High-level manoeuvring drones were virtually immune to shipboard AA systems. The US drones could simulate dive bombing which showed the dire need for autocannons. Japan introduced powered gliders in 1940 as drones but apparently was unable to dive bomb. There is no evidence of other powers using drones in this application at all. It may have caused a major underestimation of the threat and an inflated view of their AA systems.
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