We describe a 3-beam pulse-to-pulse coherent acoustic Doppler profiler (PC-ADP). The system is self contained and is using its own CPU and digital signal processor (DSP) to collect the Doppler velocity and acoustic backscatter information. PC-ADP utilizes the pulse-coherent Doppler processing which allows it to make very accurate velocity measurements combined with high temporal and spatial resolution. Tow tank tests demonstrated a single-ping velocity uncertainty of order 7 mm/s for the measurements gathered at 2 Hz with 1.6-cm resolution.