From the TV series of "Astro Boy," three episodes were selected for theater re-edition, "Robot Rocket" (46th episode), "Earth Defense Troops" (56th episode) and "The Last Day of Earth" (71st episode). Of these three, "Earth Defense Troops" was the only one originally derived from Tezuka Osamu's story "Number 7." Its settings were diverted to the "Astro Boy" series. In this film, the whole scene of "Earth Defense Troops" and a part of "The Last Day of Earth" were reproduced in color for this theater version.
[Source: Official site]