Why did the rushed 15-inch Mark I gun still prove successful?
Short answerIt was an evolution of the proven 13.5-inch system, not a clean-sheet rush design.
NotesThe success of the British 15-inch Mark I does not disprove the dangers of rushed weapons development. Engineers enlarged the proven 13.5-inch gun rather than beginning with an unfamiliar clean-sheet mechanism. That evolutionary path carried established manufacturing methods and ballistic knowledge into the larger caliber. The program still moved quickly, but it limited the number of genuinely new problems that had to be solved at the same time.