SOCAL-BRS is an inter-disciplinary collaboration designed to increase understanding of marine mammal behavior and provide a robust scientific basis for estimating risk and minimizing effects of mid-frequency military sonar systems. Data were collected using visual observations, passive acoustic monitoring, animal-attached acoustic and movement tags, photo ID, biopsy, and controlled sound exposure experiments on over 20 cetacean species in biologically important areas throughout the southern California Bight. Ninety-six individuals of ten species were tagged with six tag types, including two species [Baird’s beaked whale (Berardius bairdii), Risso’s dolphin (Grampus griseus)] not previously studied with such tools. Fifty-six controlled CEEs were conducted using protocols and protective measures to ensure animals were not harmed. Simulated sonar signals were projected through a deployed sound source and changes in vocal, diving, and horizontal movement behavior were measured. Results demonstrate that Cuvier’s beaked whales (Ziphius cavirostris) react most strongly to simulated sonar exposures with clear changes in vocal and diving behavior and avoidance responses at low received sound levels. Blue whale (Balaenoptera musculus) responses are more variable, depending on complex interactions of exposure and behavioral conditions. Ongoing efforts include expanding sample sizes in other species using simulated sounds and the novel inclusion of operational mid-frequency sonars.