On-sale date from ad in Sea Devils #4 and copyright registration.
In Amazing World of DC Comics #10, in the article "There's No Cases Like Showcases" by Jack C. Harris, he notes, "Probably one of the strangest teams in comics, Bob Kanigher and Ross Andru's Metal Men ran for four issues of SHOWCASE... The wonder robots were created (and #37 scripted) in a weekend work session trigger [sic] when editor/writer Kanigher was asked to come up with a SHOWCASE concept quickly. Too unique to be lost, the robot band was launched on a 41-issue span..."
Introduction and origin of Dr. Will Magnus and the Metal Men.
Average number of copies of each issue sold or distributed during the 12 months preceding Oct. 1, 1961: 240,000.