The hypervelocity impact (1.25 < Vi < 6 km/s) of projectiles into water overlying unconsolidated strata is reported for a variety of water depths. Variation of the background atmospheric pressure is found to be an important additional parameter. The relation of these exploratory experiments to pelagic impact of asteroidal-sized objects is discussed from the standpoint of atmospheric injection of sea water, the modification of bottom (benthic) topography, and the generation of a field of mega-amplitude sea waves and their propagation away from the source.