This is the only film in the series that was filmed entirely in black and white.
This movie marks the fourth and final pairing for both Albert Dekker and Brian Donlevy who had previously worked together in Beau Geste (1939), Wake Island (1942), and Two Years Before the Mast (1946).
Using Gammera's stated height of 200 feet as a reference, the rocket in which the scientists capture him is almost 3000 feet tall. In comparison, both the Empire State Building and the former World Trade Centers aren't even half as tall as this. So it's an incredibly huge rocket.
Given the RiffTrax treatment in 2018.