Modelling the structural response to underwater explosions (UNDEX) remains one of the most demanding fields of simulation engineering due to the limited feasibility of experimental validation. To address this, the present study compares two approaches for assessing the shock resistance of naval structures: the Dynamic Design Analysis Method (DDAM) and transient non-linear Finite Element Method (FEM) simulations. The objective was to evaluate the accuracy and applicability of DDAM as a preliminary design tool by benchmarking it against detailed FEM results. Original DDAM formulations were consistently reformulated into the SI unit system to enable a direct comparison. For the investigated tank–frame structure, the maximum effective stress predicted by DDAM was 258.3 MPa, whereas FEM analysis yielded 292.1 MPa, corresponding to a relative difference of 11.6%. These findings confirm that DDAM provides a conservative yet reasonably accurate estimate of global shock response within engineering tolerance, while FEM captures localized peaks and non-linear effects at critical joints. Thus, DDAM proves to be highly efficient for rapid preliminary assessments, whereas FEM ensures reliability in detailed evaluation of complex structural behaviour under UNDEX loading.