Diesel subs just don't make it, I speak from experience. They do not have the extended range, they are dangerous when you are charging the batteries, they have no where near the speed, their submerged time is limited and they need a lot more support than the SSNs while deployed. Our SSNs are without a doubt the quietest in the world, the soviets sounded like big coffee grinders. Talking about going back to diesel boats is like telling the Air Force to forget about the JSF and go back to P52s.