[2][3] He was a veteran staff member of the United States National Security Council, and held several advisory posts in the U.S. government and the private sector.

[2] Helmut Sonnenfeldt remained in England until 1944, when he immigrated to the United States and rejoined his parents, who had resettled in Baltimore, Maryland.

"My undoubted personal disappointment that you have almost completely excluded me from participation in or even knowledge of the more sensitive aspects of our dealings with the USSR."

[7] After leaving government service, he was a visiting scholar at the Johns Hopkins School of Advanced International Studies.

[9] His brother was Richard Sonnenfeldt, an American engineer also noted for being the U.S. prosecution team's chief interpreter in 1945 at the Nuremberg Trial after World War II.