"Gamera vs. Zigra", released in Japan July 17, 1971, pitted the giant atomic turtle against Zigra, an alien determined to take over the Earth. Groundbreaking cinema. Zigra's spaceship which looks as if it has gumballs attached to its dome, destroys a moon base before heading to Earth, where he kidnaps two children and their fathers. Then Zigra has to contend with Gamera.
The special effects make Toho's look as great as CGI, but it's a feel good movie at the very least: Aliens get destroyed by a giant earth monster.