Oxygen Destroyer

The Oxygen Destroyer was a fictional weapon that appeared in the 1954 film Godzilla. It was an extremely powerful chemical compound that was able to completely dissolve Godzilla and wipe out all life in the Tokyo Bay. It was also the only weapon that was truly effective against the monster.

Unintentionally discovered by Daisuke Serizawa during his experiments, the Oxygen Destroyer dissolved oxygen in water which instantly reduced any and all organic life within range to its skeletal frame. While it's never explained how removing oxygen causes such a destructive reaction, since the laws regarding the conservation of mass state that matter and energy can't be destroyed but only converted into another form, it's possible that the Oxygen Destroyer actually converts oxygen into an entirely different element with highly corrosive properties. In the film, Serizawa was hesitant to use his discovery for fear of the damage it would cause and political implications therein, but ultimately relented when he realized Godzilla was the greater threat. But to prevent the formula from being perverted into a wholesale weapon of mass destruction he destroyed his research documents and subsequently took his own life.

In Godzilla vs. Destoroyah (1995), it is revealed that the Oxygen Destroyer awakened and mutated Precambrian life forms that lived in Tokyo Bay that would merge together to form the strongest Kaiju ever recorded (taking Godzilla at the peak of his power, Godzilla Junior and Super X combined to finally destroy him) Destoroyah.

In the continuity of Godzilla, Mothra and King Ghidorah: Giant Monsters All-Out Attack (2001), it is disclosed that the use of the Oxygen Destroyer in 1954 was never made public and the defeat of Godzilla had been officially credited to the Japan Self-Defense Forces. This was done to spare the then newly established Self-Defense Force from public scorn after its inability to defeat the monster militarily.

Stock footage from the first Godzilla film was also used in Godzilla Against Mechagodzilla (2002) and Godzilla: Tokyo S.O.S..