This report describes research conducted to examine the application of sandwich structure technology to provide protection against the threat of an indenter striking the side or shell of a tank car in the event of an accident. This research was conducted in two phases over a 3-year period. Testing and analysis of flat, welded steel sandwich panels was conducted in the initial phase of the research. Based on the observations and results from that initial phase, a curved, welded steel sandwich panel was designed and built to protect the side or shell of a decommissioned liquid chlorine tank car during a full-scale impact test. Although the protective panel experienced severe damage, the commodity-carrying tank experienced only permanent deformation and did not puncture.