Masker-Air-System is a research for reduce underwater radiated noise and applied to battleships. it involves attaching air belts to surface ships to create air curtain by generating air bubbles. The noise from battleships can be reduced pass through the air curtain.
Fluid Silencer research to reduce fluid induced noise.
Acoustic Radiation Efficiency research for predicting and reducing underwater radiated noise
Acoustic Target Strength research is reducing the detection of submarines by sonar.