At his side, Vice-Commandant Itō took a hurried drag on his cigarette
and said, “Professor Yamane! Let me speak frankly. How can we kill
Godzilla? That’s what I want to know!”
Professor Yamane grew agitated, and the color drained from his face. “It
can’t be done! Even though he was baptized by the hydrogen bomb, he
didn’t die! He’s tenacious! And you want to kill him somehow?

Godzilla: Godzilla in Tokyo
The Underground Laboratory