Comments on 'position-tracking control of underactuated autonomous underwater vehicles in the presence of unknown ocean currents'

The control law in the commented paper is indicated to be non-causal, which cannot be applied in practical engineering directly and leads to the stability analysis incomplete. To correct the flaws, the control law is modified by solving the implicit equation in that study, and the incomplete stability analysis of the closed-loop system is finished. Finally, simulation results illustrate the effectiveness of the modified control law.