Cuvier’s beaked whales, Ziphius cavirostris, make foraging dives that last for more than two hours and to depths of more than 3,000m; these are the longest and deepest dives recorded for any mammal. The whales are particularly challenging study animals because they occur in deep water, far from shore, and spend very little time at the surface. The species is known to be vulnerable to exposure to tactical military sonars and several high-profile mass stranding events have followed naval training exercises in the Bahamas, Canary Islands and Mediterranean. Over the past five years my research group has been examining the response of these enigmatic animals to mid-frequency active sonar off Cape Hatteras, North Carolina. We have been monitoring the behavior of focal whales with a combination of short-term archival tags and longer term satellite-linked transmitters and exposing these individuals to real and simulated sonar signals in controlled exposure experiments. Our work informs the limited body of knowledge on the response of these whales to tactical sonars and has also provided new insights into their social and foraging behavior. In this seminar, I will explore some of our preliminary findings and explore how we are meeting the challenges of studying such cryptic deep-diving mammals.