Marvel Two-in-One 20 p07

Spotlight on the Liberty Legion in a crossover with the Invaders and other WWII heroes that starts in Fantastic Four Annual 11, continues in Marvel Two-in-One Annual 1, and concludes here.

When this was originally published, the timing made some sense as to whether Reed and Ben could have actually been part of the war, but that's no longer viable given the characters have barely aged during the past 50 years, making it harder for modern readers to connect with WWII stories.  But I'm old, so it still works for me!