In this study, the complicated behavior of three-dimensional (3D) water entry problems of an oblique cylinder into water is investigated using a free surface model. An efficient free surface solver presented in a previous study for modeling ricochet problems (Nguyen et al., 2020b) is extended to the 3D numerical analysis of flow problems in the water entries of solid objects. A numerical scheme is implemented on dynamic overset body-fitted grids to facilitate flow simulations of the complex geometries and arbitrary motions of objects. The numerical method is validated based on studies of grid convergence in water entry problems and via comparisons between the numerical results and experimental data in the literature. The effects of the impact velocity and cylinder-water density ratio on the motion behaviors of the cylinder are investigated. The initial conditions and cylinder density are found to have a remarkable influence on the dynamics of the cylinder, through which the physical context of the problem is more clearly observed.