US wanted to train and test new sonars against against submarines that are more silent than nuclear submarines and US don't have any. Nuclear submarines can ne

US wanted to train and test new sonars against against submarines that are more silent than nuclear submarines and US don't have any. Nuclear submarines can never be totally quiet. Turbines and pipes give out noise. Submarines with air independent propulsion can be totally silent when they stop and extremely silent when moving slowly. North Korean submarines are not a threat. Chinese diesel electric submarines are.