Is that an anti-aircraft gun or are you just happy to see me? The Sub-Mariner gets suggestive on the cover of Marvel Mystery Comics #14 (October 1940)!
By this point in American comics, I’m definitely noticing a trend of showing superheroes battling Nazis or thinly-veiled Nazi-like forces. Superman, Sub-Mariner and Captain Marvel / Shazam all have this going on by the end of 1940.