The largest and most capable submarines in Iran’s fleet are three Russian built Project 877 KILO Class boats. These diesel-electric boats are still capable although increasingly dated. They have been maintained locally and may have received some modest capability enhancements, although Iran has had difficulty maintaining some original features including the Anechoic tiles. The boats can carry heavyweight torpedoes and likely have a modest anti-submarine capability.
The KILOs are complemented by a single 48 meter long Fateh Class coastal submarine, similar in size to the German Type-206 design. This truly indigenous design carries significantly more weapons than the midget submarines while being able to operate in shallower water than most Western submarines. It can likely carry YT-534-UW1 heavyweight anti-ship torpedoes and Jask-2 lightweight anti-ship missiles. The type may have a limited anti-submarine capability although it is unclear what torpedo would be carried for that purpose. We should also assume a mine laying and special forces capability.
The Fateh followed on from the single Nahang Class midget submarine in the lineage of Iranian designed submarines. This small 24 meter boat can be armed with mines and possibly anti-ship torpedoes. It is based on Bandar Abbas on the Straits of Hormuz.
The tactic used by the Ghadirs to restrict merchant ship traffic through the Strait of Hormuz is to sit on the surface, blending in with the fishing fleet until a target is reported, then submerging to await their pray.
Current analysis suggests 14 Ghadirs in service although previous estimates have been as high as 20. Most or all are now thought to be operated by the Iranian Navy although the Navy of the Islamic Revolutionary Guard Corps (IRGC-N) may operate some.
The IRGC-N also operates two North Korean Taedong-B torpedo armed submersible boats which likely serve as long ranged swimmer delivery vehicles (SDVs) for commandoes and combat swimmers. They are known as the Kajami Class, and more recently as the Zulfikar Class, in Iranian service. They carry two 324mm lightweight anti-ship missiles.
The final type operated by the IRGC-N is the e-Ghavasi human torpedo. These one or two man wet submarines can carry a large limpet mine under the cockpit. It is unclear how many are in service.
Finally the Iranian Special Boat Squadron (SBS), part of the Marines, operate the Al-Sabehat 15 Swimmer Delivery Vehicle. This is normally launched over the side of an amphibious warfare ship and is primarily used for beach reconnaissance, but could carry limpet mines for ship attack.