Atwood was named associate director of the Boston Research and Development Laboratory of AC Spark Plug Division of General Motors (AC Delco) after the purchase. In 1961, Atwood was appointed director of engineering of Milwaukee operations of AC Spark Plug, a manufacturer of the Norden Bombsight and similar instruments during World War II. The Milwaukee operations of AC Spark Plug was made a separate division of General Motors as AC Electronics in the late 1960s, but as the space race wound down in the early 1970s, this division was merged with Delco Radio and the combined division was renamed Delco Electronics with headquarters in Kokomo, Indiana. In 1970, Atwood was appointed the Indianapolis (Indiana) Operations Manager for the newly formed Detroit Diesel Allison Division of GM. In 1974 he became the first general manager of GM's short lived Transportation Systems Division. Later in 1974 he was named general manager of Delco Electronics Division of GM. In 1978, Atwood was named a General Motors vice-president and General Manager of the Detroit Diesel Allison Division, In 1981 he was promoted to group executive in charge of the Electrical Components Group, and later that year, he was assigned responsibility for the worldwide Truck and Bus Group. In 1985 Atwood was named president of the Hughes Electronics Corporation, a subsidiary consisting of Delco Electronics and Hughes Aircraft. Also in 1985 he was named executive vice-president of General Motors and in 1987 he was made vice-chairman of the General Motors board; a member of the board's finance, executive and administrative committees; responsible for Electronic Data Systems (EDS), GMHE, and GM's Technical Staffs and GM corporate Information Management. Atwood had more than 150,000 employees under his management at that time. Two of the companies, Hughes and EDS, had founders who were high-profile billionaires.
