The
Iranian naval composition is full of "kilo-class submarines." IE: Retrofitted, Cold War-era, diesel-powered submarines. You don't need to be an expert in submarines to figure out that a diesel-electric submarine from the 1960s is
probably not going to be very quiet.
Small point of order.
Kilos are from the 80s, and
A properly maintained Kilo-class running on batteries is extremely silent. It is a rare case of the soviets building something that works and doing it correctly.
The soviets when the kilo was created realized they could not keep pace with America weapons development, so instead designed their platforms for single-puprose responses: be better than the Americans at one thing, and hope it'd be enough. (The Mig-25 is an example of this: the MiG-25 had speed and altitude performance that would allow it intercept bombers, but almost no range or dogfight capabilities.)
In the case of the Kilo, they needed a silent Hunter-Killer to counter American missile submarines (and shipping to a lesser degree) close to Russia.
The tl;dr was the Kilo Class is an attack sub meant to operate in waters where Russia had at least nominal control. You'd either be in port or on manuvers using diesel, not giving too many fucks about giving away your approximate position. When shit hit the fan you dive, go to batteries, and be nearly invisibile. The soviets put their R&D budget into acoustic paneling instead of advanced propulsion; if you were a Kilo captain and involved in a war with the Americans, you either won in which case you could safely surface and run on diesel, or you lost in which case home port was likely a radioactive crater even if you survived.
That doesn't mean Iran Kilos would be much of a threat, though.
a) Advances in active and passive sonar
b) They are almost assuredly not properly maintained.
c) Crew training is probably not great.
d) The US Navy likely knows exactly where the 3 iranian subs are at all times. Even if the sub goes dead silent, it has limited range & dive time. The Kilo was not designed to be more than a kamikaze in an attack scenario where the enemy holds the surface - especially in the comparatively shallow waters of the persian gulf.