Some info verified using a DCM scan (http://digitalcomicmuseum.com/)
The on-sale date is from the publication date recorded in the Catalog of Copyright Entries, Part 2, Periodicals, 1940, New Series, Vol. 35, No. 4.
story posits a German inciting Japanese (who are NOT quite portrayed as villains here!) to strike at Pearl Harbor...over a YEAR before it occurred in real life!
Signed on bottom right, last panel of story.