Since the Islamic Revolution of the 1980s, Iran has had two navies. One is the actual Navy and the other is the naval wing of the Revolutionary Guard. The Navy has three submarines, about 20 frigates and large patrol boats, plus some amphibious warfare and mine warfare vessels, and a lot of small, fast attack craft. The Revolutionary Guard, on the other hand, has hundreds (some estimates suggest thousands) of small fast attack craft, all under 20-meters and lightly armed.
Apparently the purpose of the Navy is to conduct conventional operations against local navies in the Persian Gulf-Gulf of Oman area. In the event of a clash with the U.S., the Navy would rapidly become irrelevant under American air attack. But the smaller vessels of the Revolutionary Guard, dispersed on the country's long coastline and among the many islands offshore, would attempt to conduct "guerrilla" operations against American warships, using hit and run and swarm attacks. The attackers would certainly take very heavy casualties. But any damage to American warships, and particularly a carrier or large amphib, would have a tremendous propaganda effect, which is probably what the Iranian leadership is really looking for.
Meanwhile, there have been some notable changes of personnel in the higher command ranks of the Iranian Navy. A submariner is now the CNO, and other submariners have been assigned to several notable posts. This is a first for the Iranian Navy, which has only three submarines. Iran is trying to expand its submarine force, turning to Russia and North Korea for boats, and technical assistance for building them. Thus, one way or another, the future of the Iranian navy is under water. While the Revolutionary Guards can make some spectacular suicide attacks, the Iranian naval officers know that the U.S. Navy is trained and equipped to deal with all these small boats. Quiet, modern, diesel electric submarines are another matter.