March 8, 2019:
Iran recently announced it had built a new type of submarine, the 660 ton Fateh. Iran claims this sub could remain submerged up to 200 meters (650 feet) for up to five weeks, apparently using a periscope type snorkel (a pipe type device to bring in air and expel diesel engine fumes) and fire locally built Hoveizeh cruise missiles (with a range of 1,300 kilometers and able to reach Israel). Hoveizeh was designed to be fired from a truck but Iran implies it has developed a version that can be expelled from a torpedo tube, get to the surface and get into the air. No evidence of that being tested yet.
Iran boasted that Fateh construction began in 2008 and the sub was built using Iranian resources and required 4.2 million manhours to assemble 420,000 components. The accuracy of all these details is dubious, based on past press releases for locally made weapons. However, Iran has been building small submarines for two decades and some have been detected in the Persian Gulf and the Indian Ocean, never far from their bases. Thus Iran has been able to use a lot of foreign submarine technology for some time. Fateh probably does exist and does work to some extent. But considering the poor reliability and performance of locally made warships the capabilities of Fateh and its weapons are probably more aspirational than actual.
In 2010 Iran announced that it had put four more mini-submarines into service, for a total of eleven built over the previous five years. Since 2000 Iran has, apparently with technical help from North Korea, been building mini-submarines for operations along its coasts, and throughout the Persian Gulf. The first two entered service around 2005. The Iranians said they would use the mini-subs to lay mines or launch underwater commando attacks. While the North Koreans provided some technical assistance, the Iranian sub was a local design, smaller than most North Korean mini-subs, which is a reflection of the more turbulent seas found off the Korean coast.
The first Iranian mini subs appear to have been based on the North Korean M100D, a 76 ton, 19 meter (58 foot) long boat that has a crew of four and can carry eight divers and their equipment, or several naval mines, or a torpedo. The North Koreans got the idea for the M100D when they bought the plans for a 25 ton Yugoslav mini-sub in the 1980s. Only four of those Yugoslav minis were built, apparently as experiments to develop a larger North Korean design. There are believed to be over 30 M100Ds, in addition to 23 of the 115 ton Iranian variation, called the Ghadir. These have two torpedo tubes and a crew of 18.
Building subs like this are not high tech and Iran is not the only amateurs going at it. Back in 2010 a drug gang in Ecuador was caught building a 30 meter (98 feet) long submarine on the bank of a jungle river. This boat was three meters in diameter and capable of submerging to about 30 meters. The locally built boat had a periscope, conning tower and was air-conditioned. It was captured where it was being assembled, and a nearby camp, for the builders, appeared to house about fifty people. This was the first such sub to be completed, but not the first to be built. Nearly a decade earlier, Russian naval architects and engineers were discovered among those designing and building a similar, but larger, boat. However, that effort did not last, as the Russian designs were too complex and expensive. It was found easier to build semi-submersible craft. But more and more of these are being caught at sea. The 2010 sub was not military grade. It could travel submerged, but not dive deep. It was built using the same fiberglass material used for the semi-submersible craft, but was larger, and had berths for six crew. There was space for about ten tons of cocaine. It probably cost several million dollars to build and was weeks away from completion and sea trials. The drug sub was similar to the small subs being built since the 1970s for offshore oil operations and underwater tourism.
North Korea has developed several mini-sub designs, most of them available to anyone with the cash to pay. Until Fateh, the largest was the 250 ton Sang-O, which is actually a coastal sub modified for special operations. There is a crew of 19, plus either six scuba swimmer commandos or a dozen men who can go ashore in an inflatable boat. Some Sang-Os have two or four torpedo tubes. Over thirty were built, and one was captured by South Korea when it ran aground in 1996. North Korea is believed to have fitted some of the Song-Os and M100Ds with acoustic tiles, to make them more difficult to detect by sonar. This technology was popular with the Russians, and that's where the North Koreans were believed to have got the technology.
The most novel North Korean design is a submersible speedboat. This 13 meter (40 foot) boat looks like a speedboat, displaces ten tons and can carry up to eight people. It only submerges to a depth of about 4 meters. Using a snorkel apparatus the boat could move underwater. In 1998, a South Korean destroyer sank one of these. A follow on class displaced only five tons, and could carry six people (including one or two to run the boat). At least eight of these were believed built and construction continues in South America.
Iran also has had some Russian built Kilo class subs. This is a 30 year old design that first entered service in 1982. So far, 70 have been built, 60 are still in service and more are under construction. It may be an old design, but it is mature and has been updated with modern electronics and quieting technology (that makes it more difficult to detect underwater.) Iran received three of these boats in the 1990s. The Kilos weigh 2,300 tons (surface displacement), have six torpedo tubes and a crew of 52. They can travel about 700 kilometers underwater at a quiet speed of about five kilometers an hour. Top speed underwater is 32 kilometers an hour. Kilos carry 18 torpedoes or SS-N-27 anti-ship missiles (with a range of 300 kilometers and launched underwater from the torpedo tubes.) Kilos can stay at sea 45 days at a time. It can travel at periscope depth (using a snorkel) for 12,000 kilometers at 12 kilometers an hour. The combination of quietness and cruise missiles makes Kilo very dangerous to American carriers. The Iranian Kilos are not used a lot because sanctions have made it difficult to obtain spare parts but using locally made substitutes Iran has kept these three boats operational. Iran has announced plans to build Kilo type subs but no such activity has been detected. For the last five years, Iran has been working on the 1,200 ton Besat but it is unclear when this sub will be completed. The Fateh may be an intermediate step in attempting a larger boat like Besat that is similar to the Kilo.