The Showa era of films run from 1954, the year where all of the Godzilla franchise began, to 1975
Gojira (1954)
King Kong vs. Godzilla (1962)
Mothra vs. Godzilla / Godzilla vs. The Thing (1964)
Ghidorah, the Three-Headed Monster / Ghidrah, the Three-Headed Monster (1964)
Invasion of Astro Monster / Monster Zero (1965)
Ebirah, Horror of the Deep / Godzilla vs. The Sea Monster (1966)
Son of Godzilla (1967)
Destroy All Monsters (1968)
All Monsters Attack / Godzilla's Revenge (1969)
Godzilla vs. Hedorah / Godzilla vs. The Smog Monster (1971)
Godzilla vs. Gigan / Godzilla on Monster Island / War of the Monsters (1972)
Godzilla vs. Megalon (1973)
Godzilla vs. Mechagodzilla / Godzilla vs. the Bionic Monster / Godzilla vs. the Cosmic Monster (1974)
Terror of Mechagodzilla / Monsters From an Unknown Planet / The Terror of Godzilla (1975)