It was the
Washington Conference (as Orr pointed out). Potsdam was held in Germany at the conclusion of the end of WWII in the Europeran Theater (the Pacific war was not yet over). It was Truman's first conference as president, and where he received word that the atomic bomb had been successfully tested in NM.
Billy Mitchell had demonstrated that airplanes, even those as primitive as they were in the 1920s,
could easily take out battleships that failed to have air cover (though some say the tests were questionably conducted). He was concerned that the Navy's investment in battleships would drain resources from naval aviation and US military aviation in general.