When I look at PLA ship construction of Submarines compared to its surface fleet, it seems submarines have received much less focus from the PLA planners when compared to the Surface Fleet. PLA Navy has vastly improved its ability to conduct Area Air Defense, Anti-Ship and Carrier Killing Capability using both land based air force and ship based missiles. They have also improved their Anti-Submarine warfare capability by having a huge number of corvettes and frigates with anti-submarine sonars and helicopters.
But compared to this level advancement, PLA submarine fleet has seen a slow development and also much less ship production.
Could it be because PLA thinks submarines are not that useful compared to surface fleets? I know SSBN is very useful for Nuclear second Strike. But what about Attack Submarines? How useful are they really compared to a surface fleet?
Attack Submarines are slower than surface ships and surface ship flotilla with a large number helicopter's can screen for subs from a large distance, so submarine's only option seems to be sneak attack and if they are detected by a surface flotilla then its game over for them.
Attack Submarines must use passive sensors to avoid detection and such sensors are weaker than active sensors used by ships and helicopters. With such weaker detection capability and speed, they cannot really detect other submarines and thus are less useful in a sub-hunter role.
So, overall, how useful are a good submarine fleet that US has? I keep reading in western articles how Virginia class is the ace in the hole for US against China since China doesn't have good submarines. But based on the limitation that submarines have compared to a carrier and destroyers, their usefulness seems to be limited.
No, as long as you avoid major sensor networks, submarines have their own strong niche.
Historically, the primary mission of the PLA has been defending against a potential US invasion, which may come most likely either in Taiwan or the SCS. For these roles, you don't need SSNs to defend. It's a luxury to have, but SSNs in shallow sea will be disadvantaged vs SSKs and historically, China had to fight closer to the shores rather than risk trying to break out behind US lines with SSNs.
And in the field of submarines, China has defintely not stood still in development, given that there's 30+ SSK that were various levels of world class when they were commissioned.
Top of the line SSKs are quieter than nuclear subs in many conditions associated with shallow water. Their main drawback is slow speed, but since historically, China knew that US forces would go to the eastern direction, the SSKs would be able to lie in wait for US SSNs and ambush them.
Nowadays, the priority is starting to change because China has more missions than just defending. Or rather, the spines of its porcupine strategy is extended from the sea of Japan all the way into the west pacific and towards Tindal. As such, a program that will quickly procure rough parity with Virginia class is needed, but it should be said that without past advancements in quieting allowing China to build the powerful SSK fleet they have, the 095 would not be a realistic project.
US submarine fleet is never underestimated by the PLA and is considered one of the major threats. However, in a defensive war, SSKs are considered able to stalemate them, while China's SSNs that have traditionally more been about keeping the tech alive would have a supporting role only.