The only weapon that I am aware of that is that fast underwater is the Russian Shkval Rocket torpedo.
http://www.fas.org/man/dod-101/sys/missile/row/shkval.htm
So- this is either Iranian bluster, or the Russians have been giving Iran some very advanced stuff.
If you read the story, you'll see there was video of the launch and impact of the weapon. You'll also see that the US Navy spokesman for the region, while not outright admitting the event actually occurred, comes about as close as they ever do to acknowledging the test.
If they only have a few test versions, that's one thing, if the Russians have provided significant numbers, which might only be dozens, of them, that changes things quite a bit. It means the carriers will have to stand off of range of this thing, or wait for the Air Force B-1s and B-2s, and maybe a few -117s for the ships that carry it, to clear the path.