A recently developed loose-coupling algorithm that combines state-of-the-art Computational Fluid Dynamics (CFD) and Computational Structural Dynamics (CSD) methodologies has been applied to the simulations of weapon-structure interactions. The coupled methodology enables cost-effective simulation of fluid-structure interactions with a particular emphasis on detonation and shock interaction. The coupling incorporates two codes representing the state-of-the-art in their respective areas: FEFLO98 for the Computational Fluid Dynamics and DYNA3D for the Computational Structural Dynamics simulation. An application of the methodology to a case of weapon detonation and fragmentation is presented, as well as fragment and airblast interaction with a steel wall. Finally, we present results of simulating airblast interaction with a reinforced concrete wall, in which concrete and steel rebar failure and concrete break-up to thousands of chunks and dust particles are demonstrated.