What really happened at Chernobyl? What we see in miniseries and documentaries clearly steers clear of technical details, or worse, was written by someone overly fond of exploring the drama but clueless on the physics, nuclear engineering and radiological problems. Then there are activists, often totally clueless, who would exaggerate the description of the damage and the potential to their own ends. This lecture attempts to separate science and engineering and actual facts from drama and activist demagoguery. It describes the Chernobyl reactor design, including its advantages and its vulnerabilities in light of other nuclear reactor mishaps. It then goes on to describe what went wrong and why. Presented by Capt. Mark McDonagh, USN/ret., a career nuclear submarine officer with BS and MS degrees in physics with 12 years’ experience at the Naval War College, now on the NSDMG staff