 From 1945 to 1946 he served as Special Assistant to the Secretary of the Navy, James Forrestal.Prior to World War II Hidalgo was a law clerk for a New York firm; after war service he resumed his career, running the Mexico City office of the legal firm of Curtis, Mallet-Prevost, Colt & Mosle before becoming a founding partner in 1948 of Barrera, Siqueiros & Torres Landa, also in Mexico, where he remained until 1965.From 1965 to 1966 he served as Special Assistant to the Secretary of the Navy, Paul H. Nitze, and then resumed legal work from 1966 to 1972 as a partner in the law firm of Cahill, Gordon & Reindel, in charge of their European office.