8.5x11" mailer letter was addressed to same fan as 1965 Supermen of America club kit, item #2137. Letter opens and has full body Superman image and DC Comics logo. Letter starts off thanking fan for letter, as a way of answering frequently asked questions and is loaded w/great content, including mention of Supermen of America club, club kit, Superman costumes by Ben Cooper, discussion of the "Five Kinds Of Kryptonite" and their effects on Superman, current Legion of Super-Heroes roster, brief Superman biography explaining his powers, and asks model enthusiasts to send new ideas to Aurora Plastics Corp. instead of NPP. Letter also brings up discussion of who is faster, Superman or The Flash, and notes the issue will likely be settled in an upcoming issue of "The Brave And The Bold." The first Superman vs. Flash race in fact took place in 1967's "Superman" #199. Additionally, the "Legion Of Super-Pets" is mentioned and members listed. Letter goes on to mention that a solo Supergirl comic book is under consideration. A list of "Famous Firsts" rounds out letter, w/chronological publication information. This letter was issued Summer 1966. Folded as issued w/some scattered aging. Fine/VF. Second letter measures 7.25x10.5" and is on NPP letterhead. Issued in late 1966, typed letter reads in part "We Regret To Report That We Have Discontinued The Supermen Of America Club For Reasons Beyond Out Control." Letter mentions returned membership fee. Single fold as mailed. Exc. Both are rare.