Beginning in 1939, he worked adviser to Paul McNutt, then head of the Federal Security Agency, and in 1940 as assistant to Leon Henderson in the Office of Price Administration (then known as the National Defense Council).

[7] In 1948, former NKVD courier Elizabeth Bentley, testifying before the House Un-American Activities Committee, mentioned Coe, whom she remembered as one of several important Treasury officials who passed on information to Silvermaster.

[8][9] Called before the HUAC (chaired by Congressman Karl Mundt), Coe denied under oath having ever been a member of the Communist Party USA.

[10] In late 1952, he was called before a Grand Jury in New York (presided over by Senator Herbert O'Conor) and then before the McCarran Committee on December 1, 1952, both of which were investigating alleged Communist affiliations of U.S. citizens working for the United Nations and other international organizations.

On the latter occasion, he declined to answer the question of whether he was a member of the Communist Party on Fifth Amendment grounds, citing the example of Alger Hiss's conviction for perjury.

Nominally, the investigation was into interference with negotiations to devalue the Austrian schilling in November 1949 as the Soviets had apparently been profiting from the black market.

U.S. officials with the European Cooperation Administration (the Marshall Plan aid agency) reported that a command came via a tickertape telecon to break off negotiations at the last minute.

Coe, who consulted constantly with his lawyer Milton S. Friedman, maintained his Fifth-Amendment plea, stating at one point that he did not want to see the blacklist extended to include those who had helped him in his search for work.

[14]: 204  Along with Solomon Adler, Sidney Rittenberg, and Israel Epstein, Coe was a translator for the fourth volume of the Selected Works of Mao Zedong.

[22] Arlington Hall cryptographers identified the Soviet agent designated "Peak" in the Venona project as "possibly" Coe, but there is no clear reason for the identification.