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The Superman production company donated this special 18 minute episode to the US Treasury to help promote school stamp day savings plans to children. This is the only episode of the series that has entered the public domain. It features all of the hallmarks that made the original 1950s Superman series so memorable.
This movie is part of the collection: The Video Cellar Collection at The Internet Archive. https://archive.org/details/StampDayForSUPERMAN