This kind of thing happens on Earth-B

Unlike Jay Garrick vs. Barry Allen or Alan Scott vs. Hal Jordan, there was never a clear dividing line between the Earth-2 and Earth-1 Batman. I don’t think there’s anything in the Silver Age that said “Batman of Earth-One wasn’t active in WW II,” it was just assumed (and logically, I think) that he was a contemporary to his fellow Justice Leaguers, which is to say not the guy in his late forties he’d be as a veteran of the Big One.

When Bob Haney and Neal Adams gave us this team-up in Brave and the Bold #84, someone at DC must have realized fans did not see Batman as their parents’ age, ergo this meeting couldn’t happen without time-travel. The house ads made that point.
(I’d show you the whole page but we’re still having image problems). Bob Haney and Neal Adams were untroubled by this.

Their story presents Bruce, the same Bruce Wayne we were reading about in Batman, as a guy working as a spy for Uncle Sam in WW II.

With the advantage of switching to his other identity in tight corners.

And while Bruce remains just as youthful in the present, the Nazi villain and Sgt. Rock, who shows up as a deus ex machina, have aged appropriately.

Obviously this worked for readers and for Haney as we got three more team-ups, though all of them were set in the present, IIRC. This story works well. It’s also a textbook example of “Earth-B,” the slang term for Haney’s willingness to deep-six continuity for his stories.

A few issues previous, we had the Spectre showing up as an Earth-One hero, without explanation. Wildcat would get the same treatment later. In Bob Haney’s Brave and the Bold Catwoman is a stone cold killer and Wonder Woman’s indestructible plane is vulnerable to ordinary artillery.

I think the Spectre crossover probably qualifies as the first Earth-B story (I’m open to counter-suggestions) but Bruce Wayne, Allied Spy strikes me as a much more outrageous example.

#SFWApro. All art by Neal Adams