The U.S. Navy has had to develop two sets of tactics for dealing with Iranian naval forces. This is largely because Iran has two navies, one very different from the other. The traditional navy exists along with a less well equipped but more fanatical forces that is a branch of the Revolutionary Guard (the personal army of the clerics that hold ultimate power in Iran). Both forces are equipped, trained, and led very differently.
The Iranian Navy has had little access to foreign ship builders in the last thirty years and has only recently become capable of building their own warships. These are crude but they float and their weapons generally work. These surface ships are small craft (1,400 ton corvettes and 2,200 ton frigates) while the submarines are of the miniature variety. There are only a few of each and construction is proceeding slowly so that, apparently, mistakes in the previous one can be discovered and fixed. Currently, the only major surface warships it has are three of the new corvettes and frigates, three elderly British built frigates (1,540 tons each), and two U.S. built corvettes (1,100 tons each). There are about fifty smaller patrol craft, ten of them armed with Chinese anti-ship missiles. There are another few dozen mine warfare, amphibious, and support ships. The three most powerful ships in the fleet are three Russian Kilo class subs. There are about fifty mini-subs, most of them built in Iran. There are several thousand marines and 20 or so aircraft and helicopters.
The “Navy of the Army of the Guardians of the Islamic Revolution” has about as many personnel as the navy (23,000, including marines and naval aviation) with about 40 large missile and torpedo boats (100-200 tons each) and nearly a thousand smaller craft, many of them just speedboats with dual outboard engines and machine-gun mounts. Up to a dozen “revolutionary guardsmen” will be found on these, armed with assault rifles, machine-guns, and RPGs. Some boats are equipped as suicide bomb craft and only carry a crew of two or three, plus half a ton or more of explosives. Some of these craft have been seen with anti-tank missiles. The “Guardian Navy” also has a few helicopters and several thousand “marines.”
Information from refugees and radio chatter indicate that the revolutionary guard naval force is mainly good for intimidation (their speedboats often come close to foreign warships and merchant vessels) and suicide attacks. This worries Western naval commanders because fanatics can be unpredictable and prone to extreme audacity. It’s not just suicide bomb boats you have to worry about but naval mines and combat swimmers (scuba divers hauling small bombs that attach to the warships and blow a hole in in the hull). On the plus side, the chances of the fanatics winning a decisive naval victory are very low but these maniacs are determined and could get lucky.
The Iranian Navy is led by officers who think along more conventional lines. Western ship commanders generally have good professional relationships with their Iranian counterparts, even when the Iranian Navy is under orders to give Western ships a hard time. If an Iranian captain radios that “he has his orders” it means he will follow through with whatever bizarre actions he has been ordered to carry out but will be apologetic about it to his foreign peers.
The Iranian Navy has fewer options than the Revolutionary Guard, simply because the navy has fewer and larger (easier to spot and hit) ships. Over the last decade the navy has generally been stationed on the Indian Ocean and Caspian Sea, while the Revolutionary Guard has been given responsibility for the Persian Gulf and protecting all those Iranian oil facilities along the coast. Actually, the Revolutionary Guard is there more as a threat to Arab oil fields and tankers because the Arabs and their Western allies have control of the air and can destroy Iranian oil fields and tankers that way.
What the Iranians hope to do at sea is create as formidable a threat as possible, even if this threat (in the form of suicidal speedboats and missile boats backed up by shore based anti-ship missiles) is short-term. In the long run, any Iranian naval power is toast.