US Ohio class in dry dock : notice the propeller blades.
http://www.ogleearth.com/2007/08/microsofts_bird.html
Due to a satellite photo leak, here's what a submarine propeller looks like, the more the merrier ! more blades means more propulsion at lower speeds thus quieter...
well it seems this design is now out of date and has been replaced with ducted pump jet propulsion since. But at least now
we know what to mod for the Cold War era :
a 7-scimitar bladed prop !
keltos