The high intensity and low distortion of underwater acoustic signals propagated to convergence zones justifies a comprehensive description and an effort toward better organization of pertinent and related information. Convergence zones are the result of SOFAR Channel propagation from shallow sources to shallow receivers. The acoustic paths are analogous to those of skip‐wave radio transmission. Although only illusive references exist in the open literature, there have been experiments showing as many as thirteen well‐formed zones spaced over a 400 mile range interval. The propagation is quantitatively predictable, and quite stable. Convergence of acoustic energy along caustics results in losses smaller by about 20 db than those encountered in a free field.

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