Upon leaving the Army, Shannon became Special Assistant for Manpower, Reserve Affairs and Logistics to the Assistant Secretary of Defense for Legislative Affairs. From June 1981 to December 1984, he was Deputy Under Secretary of the Army.
In 1989, President George H. W. Bush nominated Shannon as United States Under Secretary of the Army and he subsequently held this office from August 14, 1989, until November 23, 1993.[4] He was Acting United States Secretary of the Army from January 20, 1993, until August 26, 1993. On that date, Shannon was arrested outside the Ft. Myer post exchange in Arlington, Va. after store detectives saw him put items worth about $30 into a shopping bag and leave the store without paying. Shannon was placed on administrative leave, and never returned to his position.[5]
The charges against Shannon were dismissed after he agreed to attend a shoplifting prevention program and perform community service. He was subsequently hired as a month-to-month contracted consultant by the Deputy Undersecretary of Defense for Logistics to study inventories and advise the military on which parts and supplies to keep on hand in what quantities.[6] He completed his study and ended his contract in early 1994.[7]
Shannon later operated his own firm, Shannon Consulting Services.[8]