The general approach to scattering phenomena developed here is now applied specifically to underwater acoustic scattering problems in an isovelocity medium, for the present without absorption and inhomogeneous properties other than the various possible scattering mechanisms themselves. Among the principal new results are (1) the explicit inclusion of doppler, which is shown to produce a nonstationary frequency-modulation of the injected signal; (2) the presence and effects of two orders of inhomogeneities in the second-order media statistics, e.g., poisson, or specular point scatterers (k=1) and continuous scattering elements (k=2); (3) the coherence properties and spectrum of the specular component (k=0); (4) necessary and sufficient conditions for the applicability of the poisson model alone (and of the earlier poisson models cited in the literature); (5) conditions that the medium be a WSSUS medium; (6) for weak scattering interactions, the wave number spectra of surfaces and volumes, including the interaction of surface displacement and motion; (7) various experimental programs for the measurement and underwater remote sensing of the medium; (8) an extensive development of wave surface statistics, particularly point and directional covariances, spectra, and wave number spectra for a variety of sea surface models, including the author's recent model; (9) strong-scattering results; and (10) channel characterizations by means of the local bicovariance and cospreading functions, with specific examples