In this study, the water entry problem of a spherical - nose projectile is investigated numerically and experimentally. For the numerical simulations, a three dimensional model of the projectile with six – degree – of – freedom rigid body motion is considered. A Coupled Eulerian - Lagrangian (CEL) method is employed for modeling fluid - structure interactions. Through Eulerian - Lagrangian contact, Eulerian material can interact with Lagrangian elements. Also, an equation of state model describes the hydrodynamic behavior of the material. The numerical results are well compared with the available experimental results of a falling sphere in the literature and also the experiments of the current study. The experiments are performed for a spherical-nose projectile in a water tank equipped with a launching system and a high speed camera. The simulation results such as air cavity shape and the projectile trajectory are compared with the presented experiment data. The good agreement observed between the numerical results and those of the experiments, revealed the accuracy and capability of the proposed numerical algorithm. Also it has been shown that the pinch – off time is a weak function of impact velocity, however, increasing velocity leads to a linear increase in depth of pinch - off.