Hydrodynamic forces acting upon a model of a depth-controlled vehicle towed by a long cable were measured for all modes of motion and at various towed attitudes. Simple formulas proposed to predict the hydrodynamic forces on such vehicles were confirmed in their validity with results of the experiments and found to be useful for designing hydrodynamically good performances of the towed vehicle. Analysis of coupled motions of the vehicle towed at constant speed and the long cable was presented to study the small perturbation about the towed configuration. This method of analysis is applicable to the investigation of the stability of the vertical motion of the vehicle depth-controlled by the wing action.