We present the development of a compact, drone-compatible platform for real-time polarimetric time-of-flight (TOF) underwater imaging. Underwater environments pose significant challenges to traditional imaging methods. By integrating light polarization and depth sensing through TOF, our system enables four-dimensional imaging and mapping. Our approach utilizes a unique polarization-demultiplexing metasurface that simultaneously separates an underwater scene into four distinct polarization components, coupled with a single-photon counting TOF imager. We further develop real-time data and image processing algorithms integrated into an onboard FPGA platform capable of handling the data throughput from the TOF imager. This integrated system holds significant potential for underwater sensing applications in areas such as marine exploration, industrial inspection, search-and-rescue operations, and defense.