An underwater shock simulator has been developed for the underwater shock loading of materials and test structures within the laboratory. The tube is struck at one end by a steel projectile, with the test structure placed at the opposite end of the tube. Realistic exponentially decaying pressure pulses are generated in the water with peak pressures in the range 15–70 MPa and decay times ranging from 0.1 to 1.5 ms. The peak pressure and the pulse duration are independently adjusted by varying the projectile velocity and mass, respectively. The underwater shock simulator is used to investigate the one-dimensional fluid–structure interaction of sandwich plates with steel face sheets and an aluminium foam core. The degree of core compression is measured as a function of both the underwater shock impulse and the Taylor fluid–structure interaction parameter. Fully coupled finite element simulations agree well with the measurements while decoupling the fluid–structure interaction phase from the core compression phase within the finite element analysis leads to an under-prediction of the degree of core compression.