On sale date from the publication date and volume number found in the Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 34, 1939, Number 4. Second class periodical. Copyright number 435069. Volume number not in the comic itself.
This feature is re-named "Espionage Starring Black X" next issue.
All Gustavson credits verified and courtesy of Terry Gustafson, son of Paul Gustavson.