We break it down.
A weapon that may be closer to entering service is the Hoot (“Whale”) supercavitating torpedo, which reportedly can attain speeds of over two hundred miles per hour—around four times faster than a typical modern torpedo. This is achieved by using rocket exhaust heat to vaporize water in the path of the torpedo, allowing it travel in a gas bubble with minimal drag resistance. The first Hoot tests were broadcast on Iranian TV back in 2006, and the weapon reportedly underwent new trials in 2015 and May 2017, though the outcome of those tests is unknown. Defense analysts believe the Hoot to be reverse engineered from the Russian Shkval torpedo.
The Iranian military has long planned for a defensive naval war in the Persian Gulf, in which it would leverage its large fleet of fast attack boats toting antiship missiles to launch swarming hit-and-run attacks on adversaries in along Persian Gulf, with the ultimate goal of shutting down passage through the Straits of Hormuz.
Supporting this naval guerilla-warfare strategy are twenty-one indigenously produced Ghadir-class mini submarines, derived from the North Korean Yono class. The 120-ton vessels can poke around at eleven knots (thirteen miles per hour) and each carry two 533-millimeter torpedoes. All in all, shallow littoral waters are very favorable for mini-submarine operations, with interference from rocky shallows and loud surf reducing sonar detection ranges and giving mini submarines abundant opportunities to hide and wait in ambush. On the high end of the capability spectrum, Iran operates three much larger and more capable Kilo-class diesel-electric submarines purchased from Russia in the 1990s. These can comfortably hunt in the waters of the Indian Ocean.
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Four years ago, Iran also launched its own domestically built Fateh-class submarine. The homemade vessel may lack modern features such as antiship missiles or quiet Air Independent Propulsion system, but it does seem to be the genuine article—not something one should take for granted with reports of new Iranian weapons.