The acoustic lance is an instrument developed to obtaininsitucompressional wave velocity and attenuation (Q−1) profiles for a sedimentary layer of several meters thickness at the sediment–seawater interface. The self‐contained instrument consists of ten independent recording channels with a linear array of receivers embedded in the seafloor below a broadband acoustic source. It providesinsiturecording of full waveforms to determine interval velocity and attenuation. The system can be attached to a gravity corer or to a specially designed probe. A comprehensive experiment was carried out in Mid‐Atlantic Ridge sediment ponds where the lance madeinsitumeasurements, and core samples were recovered. Core data agree well withinsitudata in one location, but disagree in other locations. Lance data indicate that the sediment ponds have similarinsituvelocity distributions, with an acoustic channel much thinner than that predicted by earlier investigators.