Experimental data (environmental propagation loss and beam response) obtained in the Levantine Basin of the Mediterranean Sea are presented and compared to calculations performed with a multilayer, normal-mode computer model. The comparisons show good agreement between measured propagation loss and computer calculations. Beam response data show that the primary source of signal gain degradation is the bifurcated and broadened beam response. The degraded response pattern results from the combined effects of acoustic pressure field variations and motional array shape deformation. Calculations performed with the multilayer, normal-mode model show similar degraded response patterns caused by array tilting. These results indicate that system response and performance characteristics can be calculated for a specific sound channel as a function of the array shape and motion.