Here we have the theatrical trailer and three TV spots... it's fun to compare the differences between all three. I probably saw one of these spots when the movie was released. I know I saw the poster, because it's one of the weirder and creepier things done to advertise what was then considered a children's movie. I knew what the movie was when it was aired on TV in '72 or '73.
This, like GODZILLA'S REVENGE is one of the more unique films in the series. As a kid I just wanted to see giant monsters fighting and didn't really consider all the odd things about the movie that are going on. It's still one of my favorite Godzilla movies. It was also the second one I ever saw. I don't think I even wondered why he was a "good guy" now. Kids just accept things, I guess.