If the Philadelphia Experiment actually occurred, it could have been an attempt at a revolutionary military technology. The idea of making a ship disappear might have involved some sort of field generation that interacted with light and matter in a way not understood at the time. The reports of crew members being fused with the ship's structure are really outlandish, but if true, it would suggest a major miscalculation in the experiment. But again, since there's no conclusive evidence, we can only guess at what really happened based on the scattered and often conflicting accounts.