Extensive water entry experiments were performed to identify uncertainties associated with measured impact-induced loads acting on flat bottom ship structures. Of primary concern was the influence of air trapping on elastic structural deformations. The experimental measurements supplied the benchmark data suitable to validate computational fluid dynamics (CFD) predictions. Two bodies were tested. One body was fitted with stiffened, rigid bottom plating, and the other body was fitted with thin elastic plating. A large number of 30 repetitive runs recorded bottom pressures and forces acting on the flat bottom plating and monitored impact-induced elastic bottom strains. For each test case, high-speed videos of water entry sequences were evaluated. The resulting average peak values standard deviations quantified the uncertainty of these measurements.