The variation of sound velocity with depth was intensively studied at several locations in the Atlantic Ocean connected with the sound-transmission experiment of the accompanying abstract (F2). The sound velocity was measured instantaneously in situ with a sing-around type meter of NBS design. The depth was also measured instantaneously by timing the travel of the fathometer sound pulse to a connected hydrophone. For the two receiving stations NNE of Barbados, time instabilities and variation with depth of the sound velocity were statistically similar. At a given depth in the sound channel (2.5–4.0 thousand feet) the velocity varied randomly in time with excursions of a few feet per second occurring with periods of a few minutes. For measurements placed 50–100 ft apart in depth the velocity varied irregularly again to the extent of several feet per second while tracing out overall a very flat sound channel bend. This can be looked at as a randomly time-dependent multi-channel structure which gives rise to a defocusing and perhaps scattering of the ideal sound channel transmission. This effect will be exhibited using the results of ray calculation for several idealized profiles of graded irregularity. (This work was supported by the Office of Naval Research.)