 From 1937 to 1940, between his appointments as Minister to Austria and Ambassador to Cuba, he served as a US Assistant Secretary of State.As chief of the Foreign Service Promotion Board, Messersmith had to go over all appointments with President Roosevelt and learned in the process learned that Roosevelt had excellent intelligence on several foreign service officers with problems, including alcohol or affairs.While Messersmith served as United States Ambassador Extraordinary and Plenipotentiary to Cuba, he wrote a report on March 4, 1941 about the Windsors' friend, James D. Mooney, and was critical of the General Motors executive's opinions against England.