The resonant Wave Energy Converters developed by CorPower Ocean has a heaving buoy on the surface absorbing energy from the combined surge and heave motion of the waves. The WEC is connected to the seabed using a taut mooring line. It has a pneumatic pre-tension module between the mooring line and the buoy to enable a lightweight system with high natural frequency of oscillation. Phase control by the novel WaveSpring technology makes the system inherently resonant over a broad range of wave periods, strongly amplifying the motion and the power capture. The benefit is a significant reduction of the required buoy size compared to a conventional gravity balanced WEC without phase control, and improved survivability by the ability of detuning the device in storms.