The period is defined by the consolidation of the deep, refracted sound channel as a central conduit for underwater acoustic energy, enabling long-range propagation and shaping sonar and communication practices across ocean environments. The approach integrates theoretical channel models with empirical observations, reinforcing the practical value of the SOFAR concept for naval and scientific applications. Historical Significance: This era marks a turning point where ocean acoustics matured into a predictive science of propagation, noise, and clutter, establishing the framework for subsequent multi-scale modeling, beamforming, and ambient-noise interpretation that persist in modern ocean acoustics.