Traditional underwater vehicle-manipulator systems (UVMS) consist mainly of an underwater vehicle on which a manipulator is mounted. In addition to the vehicle thrusters, this paper proposes to use cables to actuate UVMSs. The main goal of this extra source of actuation is to enhance UVMS work capabilities. Similarly to cable-driven parallel robots, the cables are attached to the UVMS and a set of fixed winches permit the control of the cable lengths or tensions. We refer to this new system as a hybrid cable-thruster (HCT)-actuated UVMS. Based on the kinematic and dynamic model of HCTactuated UVMSs, this paper focuses on the determination of the available set of end-effector forces in a suitable mathematical representation. An illustrative simple planar example of HCT-actuated UVMS is also presented.