In this paper we consider the problem of mixedH2/H∞control to combine optimal and robust control for a dou-ble integrator system with nonlinear performance variables, andwe apply this to control an articulated intervention autonomousunderwater vehicle (AIAUV). The AIAUV has an articulatedbody like a snake robot, is equipped with thrusters, and canbe used as a free-floating underwater manipulator. The objectiveis to control the joints of the AIAUV to desired setpoints withoutcausing collisions between links or with obstacles in the envi-ronment. The mixedH2/H∞problem is viewed as a differentialgame, and a set of matrix equations is solved in order to constructan approximate solution to the problem for a system describedby double integrator dynamics and with nonlinear performancevariables. A feedback linearising controller is derived to obtainthe double integrator dynamics for the joints of the AIAUV, andthe solution found for the mixedH2/H∞control problem isapplied to the resulting system. Simulations demonstrate thatcollisions between links of the manipulator are successfullyavoided also in the presence of parameter uncertainties whileregulating the joints to the desired setpoints, and the methodcan easily be extended to include collision avoidance with staticand dynamic obstacles in the environment.