further future? I don't even know whether PLAN will still be developing conventional submarines...
Obviously, nobody can say for sure, because PLAN is very secretive about its submarine schedule. But, looking from the outside in, there are good reasons to maintain both conventional attack submarine and nuclear submarine development. The Wuchang shipyard on the Yangtze (where most of PLAN's conventional subs were built) has recently been expanded, suggesting to wetsern observers of an increase in diesel AIP sub production.
To see why the conventional diesel sub still has its uses, let's take a look at how diesel subs with AIP (because AIP is a basic modern standard) compare versus nuclear subs. I am making a general set of observations that are intended to be true
most of the time, and I am not comparing between two specific classes of subs.
Diesel subs with AIP
Pros:
- Very affordable on a per unit basis (e.g. German Type 214 $380 million, Type 39A Yuan class ~$300 million estimated, Soryu class $540 million)
- More stealthy on a short-term or tactical basis. A diesel sub running on its batteries is very silent, and can probably maintain this for the duration of a combat situation. Small hull size also reduces the detection range of enemy active sonars.
Cons:
- Not very stealthy on a sustained basis, because it needs to snorkel every 2-4 weeks, depending on the type of AIP.
- Limited range (constrained by fuel and food supplies, and small storage space)
- Less weapons (due to small hull)
- Less dive depth
- Very slow speed when running on AIP
Nuclear sub:
Pros:
- More stealthy on a long-term sustained basis, because it does not need to surface or snorkel.
- Unlimited range (limited only by food)
- Faster speed (25-30 knots vs. 20 knots for diesel subs)
- More weapons (especially more SLCMs)
Cons:
- Very expensive. A Vriginia class costs approximately $3 billion. Barracuda class costs $2 billion. For the price of one nuclear attack sub, you can produce 5 to 8 competitive diesel AIP subs.
- Maintenance cost if much higher.
- Can't switch off nuclear reactor, which means the reactor cooling pumps will have to keep running. This means a nuclear submarine will always produce a certain level of noise, and usually more than an AIP sub running on its batteries. Technological improvements have reduced the noise level of reactor cooling systems, but nothing beat a diesel sub running slowly on battery power yet.
The diesel AIP sub will still have a role to play in coastal waters or the near seas, where it can return to base or snorkel in relative safety. The diesel sub is also very suited to defensive operations, because it can be prepositioned in the path of advancing enemy fleets and intercept them, which would mitigate the speed disadvantage of the diesel sub. You can also mass produce them, and one nuclear attack sub is not going to defeat 8 AIP subs, in a hypothetical encounter where you don't account for the strategic advantage of the nuclear sub (e.g. in operational range).
The nuclear sub is better suited for distant waters away from home base, for offensive purposes in hostile waters, and for nuclear deterrence.