This issue has variants.
The on-sale date is the publication date reported in the U. S. Copyright Office filing found in the Catalog of Copyright Entries, Part 2, Periodicals, New Series, Volume 34, 1939, Number 4. Second class periodical. Copyright number 429173.
Indicia (transcription courtesy of Frank Motler):
Vol.1, No.1, MARVEL COMICS, Oct., 1939 Published monthly by Timely Publications, publication office, 81 Spring St., Newark, N. J. Executive office, 330 W. 42nd St., New York, N. Y. Art and editorial by Funnies Incorporated, 45 W. 45th St., New York, N. Y. Application for entry as Second Class Matter pending at the Post Office at Newark, N. J. Yearly subscription in U. S. and Canada, $1.50; elsewhere $2.00. No actual person is named or delineated in this magazine. Copyright, 1939 by Timely Publications. Printed in U.S.A.
According to Rip at the collector-society.com boards, the print runs were 80,000 on the October edition and 800,000 on the November edition.
Inside front cover. Also includes the indicia.
Five single-panel gag cartoons.
Sequence information from Joe Lovece (August 11, 2006).
First Human Torch story.
The Human Torch wears a blue uniform in this story. He doesn't adopt the Jim Hammond identity until issue #4.
Per Marvel Comics #1000, the Scientists' Guild appear next as the Three X's in Mystic Comics #1 and then as the Enclave in Fantastic Four #66.
First Angel story, character created by Paul Gustavson. The debut story resembles The Saint in New York, adapted by RKO in 1938.
All Gustavson credits from Terry Gustafson, son of Paul Gustavson.
First Namor story, reprinted from the eight pages of Motion Picture Funnies Weekly #1 and expanded with four additional pages.
First Masked Raider story, the character's name is inspired by the Masked Rider pulp magazine from 1934.
Art identification by Dr. Michael J. Vassallo of the Timely-Atlas list.
First Ka-Zar comics story, adapted from Bob Byrd's "King of Fang and Claw" (KA-ZAR pulp magazine #1, October 1936).