What happened to the US Navy's early 6-inch dual-purpose gun developed around 1938?
Short answerIt was ahead of its time: the dual-purpose idea was sound, but the initial technology became a dead end and needed major reworking.
NotesThe 1938 US Navy 6-inch dual-purpose gun was an idea that arrived before its supporting technology was ready. The combined surface-and-air role still had value. The initial design became a technological dead end and required substantial reworking. A sound operational idea can outpace practical weapons engineering.