In World War I John L. served as an ordinary apprentice seaman. Years later, as assistant secretary of the Treasury under President Franklin D. Roosevelt from 1940 to 1944, he participated in developing, and was the principal envoy to congress on significant tax legislation and was an important voice in the effort to sell war bonds, both critical to the financing of World War II. A man of principle, Sullivan courageously resigned in April 1949 to publicly protest the decision of the new secretary of defense, Louis Johnson, to suddenly cancel - without consultation with the Navy - the construction of the United States, a new aircraft supercarrier, calling Johnson"s act detrimental to the nation"s future defense.