Sealion was one of, IIRC, the earlier alternative history tropes, along with the rebels winning the American Civil War. It's been done to death, but some people hope to find new changes to ring on it. It's also one of the few that non A/H folks may have heard of. I feel confident that a lot of other folks have tried it, too.
My first attempt at A/H, back in 3rd or 4th grade, was a dreadful version of Sealion, with a dismal failure for the invaders.