Supergirl Revealed

Once, Supergirl (Kara Zor-El), after arriving on Earth from Argo City, was kept secret from the world by her cousin, Superman.  

Superman put her in an orphanage as Linda Lee, and she later adopted by the Danvers, becoming Linda Danvers.

But, that all changed this day, according to the old DC calendar, today was the day Superman revealed her existence to the world in Action Comics #285 (February, 1962, under a cover by Curt Swan and George Klein), with a story by Jerry Siegel and Jim Mooney.

Supergirl first appeared back in Action Comics #252 (May, 1959), reprinted in Secret Origins #2 (April-May, 1973), and this issue, plus a few that led up to it were collected in a giant Action Comics #360 (March-April, 1968) (and follow the links to read more on them!).