Abstract The impulse of the shock wave from an underwater explosion, as recorded under laboratory conditions, has been used to predict the signal strength of heterogeneous explosives of the nitro-carbo-nitrate type used in offshore seismic exploration. The changes in relative magnitude of the shock-wave impulse due to changes in composition and to varying shot-firing depths are reported; compositions that maximized the impulse were found for a mixture of aluminum, dinitrotoluene, oil, and ammonium nitrate. Increasing shot-firing depth from 6 to 9 ft increased measured impulse 16 percent for charges having identical weights and compositions.