Underwater acoustic imaging applications such as mine counter measures and sidescan seafloor surveys would benefit from an operational synthetic aperture sonar system. While the potential of high-resolution synthetic aperture (SA) sonar designs to provide unprecedented detection and discrimination performance is clear, the real-world issues of residual platform motion and temporal/spatial variations in sound speed (SSP) have prevented operational deployment of existing designs. High azimuthal resolution requires a synthesized aperture of lengths approaching ten thousand wavelengths. This imposes a tight constraint on residual motion error and the ranges of environmental scenarios where present designs can operate. Synap Corporation has developed the reduced wavenumber synthetic aperture (REWSA) algorithm/design based on an interferometric preprocessing stage operating on multiple element baseband receptions, and a unique inversion stage. The REWSA algorithm is shown to have a reduced wavenumber characteristic that is inherently robust to the effects of the sonar environment. Discussion of resolution, spatial sampling, and aperture requirements will be supported by simulation and experimental data results. [This work was sponsored by NOAA under Contract 50-DKNA-5-00206.]