An active control strategy is applied to the WaveSub Wave Energy Converter (WEC). The purpose of the control strategy is to maximise power capture across a range of seas whilst operating within physical system constraints. WaveSub uses four rotational PTOs attached to drums which are driven by taut tethers connected to a float. The full scale WEC has been modelled in the WEC-Sim environment using a fixed passive damping system for the PTOs, which was optimally tuned for individual sea-states to provide a performance benchmark. An active control system utilising the simple and effective method with a Linear Quadratic Regulator velocity tracking loop is developed. A range of sea states is applied and the performance of the active and passive systems compared. Power gains of 13% to 86% are observed across a wide range of irregular sea states compared to the optimally tuned passive system. This approach shows promise to provide a substantial increase in power capture for a minimal additional device cost and therefore a significant improvement in cost of energy would likely result.