The dynamic response of a ring-stiffened circular cylindrical shell, immersed in a fluid and subjected to a suddenly applied radial load, is investigated. The shell is infinitely long, the stiffening rings are periodically spaced and identical, and the applied load is uniformly distributed. In the analysis, the authors employ a technique involving the superposition of steady-state solutions which they have found, in previous applications, to be more suitable for problems involving complex interaction conditions than the customary transform approaches. The shell response is computed for an applied step pulse. Displacements and stress histories, and variations in their peak levels, are presented for values of ring flexibility, mass, and spacing, varying over a broad range. The response to the dynamic load is also compared to the response obtained for a static load of equal amplitude. It is found, for example, that for a given ring spacing and flexibility, increase in ring mass above a certain level can lead to dynamic stresses and displacements that exceed their static counterparts by large amounts. Such a situation also makes the existence of an oscillating response more likely. When the ring mass has a negligible influence of the shell response, the trends followed by the peak dynamic displacement and stress with ring flexibility are not appreciably different from those followed by the corresponding static quantities. A similar observation can be made concerning the variation of the peak dynamic displacement with ring spacing.