"Undersea Kingdom" is fast-moving and exciting, better than most serials...with the added fun of seeing how the cliffhangers are impossibly resolved. One of my favorite superheroes who's never been filmed is Namor, the Submariner and this serial comes closest to rendering him on film. It's amazing how a very ordinary looking guy (Ray Corrigan) with an admittedly great physique can be transformed into a thrilling superhero just by donning a costume. This is the best example of the transformation by costume...Corrigan doesn't look anywhere near as imposing without that great sort of Aztec-looking helmet, the best flowing cape (far better than Superman's) and those nifty fish-scale briefs that turn transparent when the lighting hits them just right. Fortunately, our hero wears this impressive outfit throughout most of the series, and you will notice how much his presence is diminished just by removing the helmet from time to time. Despite the robots that look like lumbering water heaters and a sardine-can tank that announces its presence with an ambulance siren, this is a classic serial adventure that should surely please most action-hero and serial fans. It's a very ambitious and largely successful product for its times, with the added bonus of little of the tediously long previous chapter replays of later efforts in the genre. Highly recommended!