Pep Comics #7, featuring the Shield (the very first patriotic themed superhero).
The Shield predates Captain America by over a year (appearing in January 1940, whereas Captain America first appeared in March 1941). Cap first appeared with a triangular shield, which was quickly changed to a round one when the publisher of Pep Comics threatened a lawsuit because it resembled too closely the Shield’s costume. The Shield lasted until 1948, after having lost the lead spot in the book to Archie Andrews of Riverdale, as Pep Comics went from a superhero title to a comedy book.
Still, there are some dramatic covers associated with the character (such as this one).