Diesel-electric. They cruise around just under the surface on diesel, with snorkels to bring in air and expel exhaust. But, then they can shut down those diesel engines, fully submerge, and maneuver on batteries for a few days and maybe a hundred miles.

While they are on diesel engines, they are loud, and stuck to the surface. While they are on batteries, they are silent. For the few days that they are submerged, they are quieter than our nuclear subs.

Yeah, they pose a potential threat to a carrier group, but the “proportional response” to attacking a carrier would be the destruction of every naval facility they have, so not exactly a serious threat.

I don’t know anything about Iran’s subs, but Sweden’s famously stealthy diesel subs keep a big tank of liquid oxygen on board and mix the exhaust with seawater before releasing it

Diesel subs use snorkles when using their engines and batteries for silent running. They work a lot like diesel/electric trains, in that the diesel engine is acting more like a generator for an electrical engine.

IIRC from my C:MO experience, diesel subs (at least Greek ones that is) only use diesel above surface, and use batteries when submerged

The short answer is “it’s complicated but yes, and practically no.” Nuclear submarines have the operation range to obfuscate their location orders of magnitude better than diesel. Diesel is quieter but their range makes tracking infinitely more feasible. “A needle in a haystack vs a splinter in pail of hay.” Nuclear is better at power projection, diesel is better at short range defense/offense.

Look at it this way: When a diesel sub is endangered, they can turn off everything and I mean EVERYTHING. Quiet as a mouse that doesn’t exist. However, it will have to resurface eventually. A nuclear sub cannot do that. The cooling pumps have to keep running. But they can stay under water pretty much indefinitely (until they run out of food).

Nuclear is quieter than diesel, but louder than electric. Diesel subs are on diesel for transit to/from their patrol area, and on battery for their short-range patrol. Nuclear subs are much quieter during transit, but slightly louder during a long-range patrol.

Nuclear subs have to continuously pump cooling water; diesel-electrics can shut down pretty much everything that makes noise.

Nuclear subs have cooling systems that need to be working constantly. This creates additional vibrations/noise on top of the propulsion system.s that would be pretty similar between both subs. As well as nuclear subs needing to be much bigger, so require propulsion that produce more noise

Diesel submarines can literally turn off every system and just drift in the ocean currents silently, or loiter on the sea floor where they are indistinguishable from a rock.

Worth noting nuclear submarines have a sort of minimum-practical-size determined by the need for a functional nuclear reactor on board. Combined with the plain expense of nuclear reactors means that states can build way more ssk’s than ssn’s for a given budget. It’s often better to have three 25% chances of sinking the other guy than one 50% chance.

Unless you have access to intelligence that you probably shouldn’t be sharing in an Internet forum, neither of us really knows what is needed to guide the missiles of our adversaries.

That said, my day job is a GNC engineer (guidance navigation and controls) for rockets and spacecraft. It’s absolutely possible to hit a carrier with no radio signals whatsoever

I would rule out drones, as yep, if they are radio controlled, you can just blast them with jamming, but guided missiles are absolutely capable of sinking a carrier. The trick is that you need a shitload of them since the carrier group has both long-range missiles and short range CIWS systems to counter those missiles. The only way you can hurt a carrier with them is if you launch a shitton of them.

Or you can actually launch ballistic missiles instead of cruise missiles. The upside is that anti-missile missiles and CIWS are not quick enough to catch them and radars can’t really see them if they are not Hamas-style homemade fireworks, but stuff like the Kinzhal. The downside is that it’s very hard to guide it in the terminal stage, so they might come very fast, but may be very inaccurate.

If Russia’s Kinzhal, or China’s DF-ZF is accurate enough to hit a carrier, that’s a big problem for the carrier. Whether it is accurate enough is a good question, since maneuvering something that is that fast is not easy, and also if you go that fast in our atmosphere, you are basically blind since the air gets turned into plasma around you (think Space Shuttle reentry). It is a hotly debated topic whether Russia’s or China’s weapons are accurate enough. OTOH, from the price of a carrier (not including the group or the planes or operation), you can build more than a thousand Kinzhals, so assuming you can launch them all, eventually it might hit something important.

Or you can also just build a diesel electric sub, get some cheap guided torps and torpedo the shit out of the carrier. There is ASW defenses of course, but Sweden has repeatedly demonstrated simulated kills on US carriers with diesel-electric subs.

Yeah tell that to the Iron Meme system.

For the cost of one guided rocket you can throw enough cheap trash to empty the entire carrier defense systems.