For a preliminaly design of a depth and roll controllable towed vehicle for ocean measurements, three dimensional numerical simulation techniques for calculating motions of a towed vehicle and towing cable are developed. The hydrodynamic coefficients of the towed vehicle and towing cable used in calculations are obtained from experiments in a circulating water tank. The towed vehicle is developed to house a CTD (Conductivity, water temperature and depth) sensor and an acoustic doppler current profiler. The CTD sensor needs the accurate depth control and the current profiler demands a high level of stability in pitch and roll of the towed vehicle. In the design of the towing system and towed vehicle, the special attensions are paid to meet these requirements. The angles of main wings and horizontal tails are under feedback control in order to maintain operation depth and roll stability. The results of numerical simulations confirm the good performance of the system.