One thing that always helps me buy into a superhero scene is the presence of capable, competent non-superhumans backing up the superhero in their fight against evil. From the Avengers battling aliens alongside NYC cops and National Guard, to Wonder Woman spearheading an assault across no-man's-land, the involvement of soldiers and/or law enforcement (or even civilians, though that's a good bit rarer in our militaristic culture) helps add some weight and scope to superheroic do-goodery.
So with that in mind, I've grabbed some WWII plastic kits, with an eye towards building some late 1930s troops. With head swaps and a bit of conscientiousness about their weapons, I've made and painted my first marine and first army infantryman (with an unconverted Pulp Figures gangster for comparison).
Both soldiers are made from the appropriate Warlord Games kit. The marine has a head from the AWI Continental Infantry kit, with the crown of the hat cut down a bit to look more like a campaign hat. The army man has a brodie-helmeted head that I bought from Anvil Industries. I don't know if the rest of their kit is strictly accurate for 1938, but I think the heads do a good job of signifying "not 1942 yet!"
I rather like how these two turned out, so I will be painting the rest of their squads soon.