Abstract: After being vertically launched from an underwater platform with a lateral transport velocity, a vehicle navigates with a finite angle of attack, during which the hydrodynamic forces acting on the vehicle, together with its motion responses, play a critical role in determining its attitude stability as well as its trajectory safety. In this work, the dynamic characteristics of an underwater-launched vehicle are investigated both experimentally and theoretically. Experiments are conducted at different transport velocities by means of an underwater launch facility, within which the motion parameters are recorded using embedded measurement units installed inside the vehicle. The underwater trajectory, the pitch attitude, as well as the corresponding force coefficients, including lift and pitching moment, are quantified under different initial launch angles of attack, thereby enabling a detailed characterization of the motion response. A dynamical model for underwater motion with a finite angle of attack is developed based on potential-flow theory in combination with a slicing method, in which the overall hydrodynamic forces and moments are obtained by modelling and summing the contributions of potential cross forces, viscous cross forces, axial forces, added masses in both the axial and lateral directions, together with the added pitching moment of inertia over all slices distributed along the vehicle body. Through this formulation, the spatial distribution as well as the temporal evolution of the hydrodynamic forces acting on the vehicle are elucidated. For vehicles with an ellipsoidal nose, the peak cross force acting on the nose in the early stage is found to exceed that on the cylindrical section by more than twenty times, which, although decreasing thereafter, remains dominant in both the lateral force and the pitching moment. This disparity is observed to be even more pronounced for vehicles with a conical nose, thereby resulting in larger pitching moments. In addition, the temporal evolution of the angle of attack, the lateral force, and the pitching moment during the underwater motion is clarified. In addition, the temporal evolution of the angle of attack, lateral force, and pitching moment during underwater motion is clarified, all of which decrease rapidly in the initial stage after detaching from the launch tube and then gradually level off or even exhibit a slight recovery.