I've had an idea for a stealth submarine that uses vertical vanes to eliminate sonar reflections in the same way as the protusions on the walls in an anechoic chamber. The ship is mainly flat based on a ray shape, to minimise horizontal or frontal reflections and the engines are hollow tubes with screw threads (Archimedean screw) to minimise sound output. The vanes themselves could detect vibrations, making those a sort of sensor.
