Operation Showdown occurred in the early 1980's and targeted the East German Intelligence Service, utilizing a Navy civilian employee as a Double Agent. In November 1983, East German physicist Alfred Zehe was arrested in Boston and later pleaded guilty to espionage.
(From: http://ncisahistory.org/wp-content/uploads/2017/06/NCIS-Recruiting-Brochure-This-is-the-NIS-Early-1980s.pdf)
Bill Tanner, a double agent working for the FBI and the Naval Investigative Service, began a sting operation by walking into the East German Embassy in Washington DC and offering to sell classified information he obtained while working as a civilian engineer at the Naval Electronic Systems Engineering Center in South Carolina. The operation ultimately lead to the 1983 arrest of Alfred Zehe.
(From: https://books.google.com/books?id=l_ZTCgAAQBAJ&lpg=PA88&ots=VOvtDnkHTp&dq=bill%20tanner%20double%20agent&pg=PA88#v=onepage&q=bill%20tanner%20double%20agent&f=false)
Historical Dictionary of German Intelligence by