We address the control design problem for stabilization and tracking of Unmanned Sea Surface Vehicles (USSVs). To this end, we describe the design and implementation of a high-accuracy real-time Six Degree-of-Freedom (DOF) Hardware-In-The-Loop (HITL) simulation platform for use in development and evaluation of controllers for USSVs, The HITL platform incorporates a nonlinear dynamic model of the USSV, emulation of sensors and instrumentation onboard the USSV, and the actual hardware and software components used for control of the USSV in the experimental testbed. Detailed models of hydrodynamic effects, actuators including thrusters/propellers and control surfaces, and disturbances including ocean currents, waves, and wind are included in the dynamic simulation. The fidelity of the developed HITL simulator is demonstrated through comparisons with experimental data collected from a USSV. We also propose a nonlinear backstepping-based controller for stabilization and tracking for USSVs and present closed-loop results from HITL simulation and experimental testing.