Following detonation of an underwater explosion, sound reverberates from the ocean surface and bottom and from scatterers within the medium itself. In addition, the ocean basin and obstructions within it, such as seamounts and islands, reradiate the acoustic energy incident upon them. This paper describes a computer model developed to predict the sound level that will ensue following detonation of a large underwater explosion as a result of this latter basin boundary reverberation. Experimental data from 10‐ton shots fired a number of years ago in the North Atlantic were used in the development of the computer model. The model has now been tested by comparing predictions with results obtained from CHASE XXI, a 660‐ton North Atlantic shot. This simplistic model has proved adequate for matching available experimental measurements in the North Atlantic Basin. Since the parameters on which the model is based are simply defined and applicable to any geometric configuration, the computations are expected to apply to other ocean basins as well. [Work supported by DNA.]