Upon returning to the United States, Bernadou was assigned to the recently revitalized Office of Naval Intelligence (ONI). There, he went to work studying world economic conditions with a particular emphasis on the world's supply of nickel ore. The importance of that commodity resulted from the navy's adoption of nickel-processed steel for its new ship construction. He also collected information on foreign seaports, assisting in the writing of a book on international ports and coaling stations. His facility with foreign languages put him in an ideal position to translate articles of value to ONI from French, German, Russian, Swedish, Spanish, and other languages.