Abstract: A subsea well installation is equipped with means for performing required control functions as directed by electrical command signals transmitted over a primary cable from a remote surface location. The subsea installation includes a logic system which effects desired normal or emergency control functions according to self-contained programs or in accordance with instructions received from the surface. Multiplexing means at both locations substantially reduce cable dependency and reduce the number of electrical conductors required in the cable. Cable dependency and signal traffic are further reduced by the provision of self-contained means in the subsea logic system which verify that correct instructions have been received without need for retransmitting the received instructions to the surface. When the primary cable is damaged or communications are otherwise interrupted, a special subsea logic is initiated to control operation of the well installation and a submerged buoy is automatically released.