I want to know the answer to the following question:
What did the US Navy rely on?
All the background I'm provided with is that "Worst of all, before the war, an uninformed US Customs officer had seized a copy of the Japanese merchant marine code (called the "maru code" in the USN), not knowing that the Office of Naval Intelligence (ONI) had broken it.". Is that enough to answer the question?
Answer: no