Iran Claims Successful Test-Fire of High-Speed Torpedo

Possibly a reverse-engineered Shkval fired by the Iranians.

Iran's navy said it successfully test-fired its fastest torpedo capable of reaching a maximum speed of 360 kilometers (223 miles) an hour, the official Islamic Republic News Agency said.
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The new torpedo is about three or four times faster than a normal weapon and as swift as the Russia-made VA-111 Shkval, the world's quickest underwater missile, which was developed in 1995, the Associated Press reported, without saying where it obtained the information. It isn't known whether the torpedo is capable of carrying a nuclear warhead, AP said.

And it's probably only effective with a nuclear warhead, because it likely has no internal guidance. The nuclear-capable shkval was designed as a battle group buster, fired from long range at high speed in the general direction of the carrier.