1. Introduction
Acoustic target recognition is the process of identifying sonar detectable objects, such as ships, submarines, or vehicles, based on their acoustic signatures, in the absence of direct visual cues. Acoustic target recognition is the basis for many modern, non-visual methods of detecting and 10-cating objects underwater and remains a critical technology for both military and civilian applications. For instance, in naval missions, it is crucial to have the capacity to detect acoustic signatures in real-time passively, such as vibrations, system mechanical noise, sounds of the natural environment, and, most importantly, underwater and surface sounds of ships. The application of underwater acoustic target recognition is not limited to defense; it can also be applied to the mineral industry, deepwater drilling and marine life monitoring. However, the classification process can be extremely challenging due to the inherent characteristics of underwater transmissions, including the time and space variation, signal attenuation, low signal-to-noise ratio (SNR) and the diversity of underwater target features.