Alternate Ending wasn't much better
I read somewhere that in the original ending the globe sends Sinise into the big steel harpoon which made audiences laugh. There was some sort of tidal surge that flooded the tunnel at some point. That doesn't sound much better.
Commander Kevin Dunne discusses 1)his memories that men don't drown quietly, 2)he hasn't been on a sub since "the insident", and 3)the song playing during the closing credits mentions "drowning men don't die quietly". So why didn't Dunne just get trapped in a flooded tunnel while Officer Rick Santoro has to hear him drown as a result of his choice? Wouldn't that have been dramatic?
Perhaps this is why DePalma voiced irritation at the influence of the studio system on this film. I read somewhere that he said, "everyone has an idea of what should be in the script."