A multibeam subbottom profiling system (MSBPS) is being built with funding from the Defense University Research Instrumentation Program (DURIP) in coordination with the Office of Naval Research. The MSBPS is being constructed from three T70 Neptune Sonar transducer modules in a line. Each T70 has five 11.5-kHz elements in each of two parallel lines. The resulting system is composed of 15 elements in each line with a total length of 1.3 m separated by about 8.5 cm. Each line has full beamwidths to the 3-dB points of about 5×70 deg. The system will be used in an interferometric mode between the two lines. [This work is supported by ONR 321OA.]