To date, undersea optical communication has been driven by wide-beam LED systems. Directional laser systems have several advantages | increased range, increased data rate, and better performance in solar background | but require a precise tracking system to maintain laser pointing through vehicle motion. We have demonstrated an underwater laser communication system with a bi-direction, all-optical pointing, acquisition, and tracking system. Laser communication terminals were mounted on two remotely operated vehicles that were piloted to the ends of a pool (a separation of 20 m), coarsely aligned to within about 10 degrees, and then set to autonomously acquire and track each other. Acquisitions occurred within a few seconds, and the link never broke during maneuvers. To our knowledge this is the first demonstration of a functional undersea laser tracking system between mobile vehicles. The demonstrated precision and robustness can enable 1+ Gbps data links between independent, moving vehicles, over several 100 meters in clear ocean water. Additionally, this approach provides precise (cm- class) relative positioning between the communicating parties, enabling relative position, navigation, and timing (PNT) distribution between independent vehicles. This technology is a crucial enabler of undersea wireless optical networking for manned and unmanned vehicles.