Dannenberg was one of the original German rocket scientists from Operation Paperclip, brought to the United States by Wernher von Braun.
Originally, the scientists were brought to Fort Bliss, Texas, to work for the U.S. Army. Later, Dannenberg transferred to Marshall Space Flight Center in Huntsville when NASA was formed.
He served in several roles, including deputy manager of the Saturn program, and retired from Marshall in 1973, but remained in Huntsville with his second wife, Jackie.
His first wife, Ingeborg, passed away. They had a son, Klaus Dieter, who has two married children. From them Dannenberg had four great grandchildren.