Anyone who attempted to behead the Hydra found that as soon as one head was cut off, two more heads would emerge from the fresh wound. To defeat the Hydra, Hercules called on his friend Iolaus for help. As soon as Hercules cut off one head, Iolaus would seal the wound with a hot iron or a torch so that nothing could grow to replace it. After removing the Hydra’s immortal head, Hercules buried it under a large rock.
The “Hydra” during WWII was referring to the Nazi War Machine. There were several reasons for the D-Day Invasion. One of those was because the infrastructure in the Reich was hard to tear down and keep down by the allies. If a major target was bombed, the Nazis would build it back up again. If the allies bombed it again, the Nazi would reinforce the structure, the allies would bomb it again, the Nazis would then build the structure underground. The invasion was the only way to get to the heart of the Hydra.( Nazi Technological Invincibility) Hitler was the immortal head of the Hydra that had to be cut.
The allies not only fought Hitlers soldiers, but Hitlers scientists as well.
I scanned one of my magazines to give you an idea of what some U.S. officials thought of the Hydra.
Hydra’s First Appearance in the Marvel Universe:
Strange Tales #135 (1965)