A new type of technology might currently be in development by China, that could lower the acoustic signature of submarines. In a traditional submarine, a propeller is attached to a driveshaft which is turned by a large engine or hydraulic system. These types of systems rely on a great deal of machinery and moving parts, both create lots of noise in an environment where stealth rules supreme.
In the "Silent Service", making as little noise as possible to evade detection is always the goal. To that end, a new concept in propulsion called a “Rim-Driven Propeller” or RDP (also known as a Rim-Driven Thruster or Rim-Driven Pumpjet) is being considered. An RDP removes the hub, driveshaft and gearbox from a submarine’s typical propulsion system, thereby giving the sub even greater stealth.