Let's put it this way-a N-sub will slaughter any number of D/Es in deep ocean by virtue of it's ability to stay submerged for great periods,at great depts & much greater speed & with increased efficiency of it's sonars.Nearer to the shore(in littorals),the situation becomes a lot more hazy,with speed & dept not as useful.
Tom_Paine,the Kilos that China are acquiring from Russia carry a new cruise missile system(in anti-ship & land attack variants) with ranges from 220kms to 300kms.So It doesn't even need to go out of port to hit Taiwanese vessels.
From what I have read, submerged endurance of a normal D/E doesn't go much beyond 24-30 hours due to the need to recharge it's batteries.The current D/Es that China is acquiring from Russia reportedly feature an air-independent propulsion module which can theoritically allow the sub to stay submerged for upto 8-10 days(which is a huge advantage for a D/E).If & when the Germans start selling to China,the PLAN would have it's eyes on Germany's Fuel cell based AIP,which according to reports can sustain a sub underwater for as long as 15 to 20 days & is more efficient than competing Russian & French systems.
"the US Navy in the forefront -- find themselves ill-equipped to counter the explosive growth in the Third World fleet of stealthy, fourth generation diesel-electric subs like the U-212/214-class (Howaldtswerke-Deutsche Werft GmbH of Kiel and Thyssen Nordseewerke GmbH of Endenand, Germany) and the Scorpene-class (DCN of France and Izar (formerly Bazan) of Spain). Such current technology subs can stay submerged for days without need for snorkeling. Equipped with closed-oxygen diesel drives such as the French "MESMA" (Module d'Energie Sous-Marine Autonome) AIP steam-turbine system that burns ethanol and liquid oxygen to make steam to drive a turbo-electric generator, the design permits retrofitting into existing submarines by adding an extra hull section. Typical cost for a new submarine powered by MESMA is $250 million. These warships are openly for sale to almost anyone with a big enough checking account (except Taiwan, but that’s another story). For the budget-conscious – or someone simply in a hurry to raise hell with an allied navy -- a Russian P-130 or Piranha-T Small-class submarine may be purchased for a fraction of the cost of a Scorpene. While limited in crew size and range, a Piranha-T’s torpedoes and mines are quite suitable for denying coastal waters to most navies ill prepared for ASW."
"Today’s conventional subs – SSKs -- with their “airless” diesel technology, super-quiet electric motors, greatly improved noise reduction, and great submerged dash speed in shallow water, make active ranging in most cases almost useless. The halving since 1991 of the US Navy’s submarine fleet -- a primary ASW asset itself – further aggravates the situation. The US and allied navies have become keenly aware of this danger. ASW, like anti-mine warfare, has traditionally been unglamorous, complicated, and absolutely essential to the Navy. There was no movie “Top Bunk” starring Tom Cruise as P-3 pilot Hank “Sleepy” Levey on a typical 12-hour flight looking for submarines in the middle of the Pacific Ocean, the dramatic highlight of which was two off-duty crewmen flipping a coin over one bunk."