The Institute for Defense Analyses IDA is a not-for-profit company that operates three Federally Funded Research and Development Centers FFRDCs. We perform scientific and technical analyses for the U.S. government on issues related to national security. Recently, we performed a numerical analysis for the Strategic Environmental Research and Development Program SERDP to explore the fidelity of computational models for predicting the initial penetration depth of Unexploded Ordnance UXO in underwater sites. This briefing discusses the details of our analysis. A separate briefing provides a shorter summary.