ABSTRACTA detailed investigation of the control problems involved in an active fin roll stabilization system has been undertaken which has resulted in an improved and greatly simplified system.Transfer functions were derived to describe the dynamic performance of a ship in roll, the active fin servo system and the control signal generation process. Analogue computer simulations have examined existing systems and alternative methods of control signal generation.An optimum system has now been derived taking as its sole input, a roll angle signal from the ships central weapons stabilization system (Mk. 19 compass). This signal is processed electronically to derive a control transfer function in terms of roll angle, roll velocity and roll acceleration. Other features e.g. forced roll, stabilize with list, speed compensation of loop gain, helm compensation and fin limiting as a function of ship's speed, are incorporated as are testing and fault finding facilities, and static and dynamic calibrating signals.The system has been proved by breadboard models driving a computer, and at sea; a prototype has also been tested at sea. New system cost is about 50% of that presently in service and predicted reliability is much higher due mainly to the elimination of inbuilt gyros and electro/mechanical computing methods.