Superman #115 (1957)

THE MIDGET SUPERMAN When a midget actor playing Superman grows to normal size overnight, Superman summons a pre-teen Super-Tot to take his place, while waiting for the growth spurt to reverse itself. JIMMY OLSEN'S LOST PAL Superman undertakes a dangerous mission and gives Jimmy Olsen an envelope containing his secret identity, to be revealed if he doesn't come back for a week. A criminal disguise artist plans to learn the secret for himself. THE THREE SUBSTITUE SUPERMEN Superman undertakes a mission in space, leaves his uniform behind, and allows Perry White to use a power-endowing machine to create three successive substitute Supermen.