In the previous papers, a set of fundamental equations of motion for a submersible was derived in order to analyze the motion characteristics, and the relationships between the motion characteristics and the design parameters were investigated. This paper deals with the research on the relationships between control system structure in longitudinal motion and design parameters of the submersible, that moves at constant speed along the orbit where a series of measuring points is prescribed. First, the state equation in the longitudinal direction suitable for the body design is derived. The control system of the submersible is provided. Quadratic function is defined so as to estimate the control performance of the motion. Finally, the kind and the range of design parameters are determined from the engineering standpoint. The main results are obtained as follows. (1) Even if a sudden change of the direction of water current occurs consistently, the submersible can be controlled to move along the demanded orbit by utilizing a regulator composed of the state variables. (2) The state equation can be decomposed in two parts ; one is the equation expressing surging motion, and another the equation expressing both heaving and pitching motions if the submersible design is satisfied with conditions for improvement of idealized controllability. (3) 15 design parameters are derived from the coefficients of the state equation. (4) The submersible which is designed symmetrical around the body axis is controllable to the large extent of deformation. (5) The control system is lack of observability, in the case that nondimensional time constant of the steering apparatus is approximately 2.1. It is concluded that the method to obtain the relation between the design of submersible and its performance applying to the optimal control has been established and that the indispensable knowledge to quantitatively evaluate various kinds of submersible has been provided.