Dr. Michael Callahan is a Program Manager for Biodefense and Mass-Casualty Care at the Defense Advanced Research Project Agency (DARPA) and an Associate Physician at the Division of Infectious Diseases at Massachusetts General Hospital/Harvard Medical School. Current wilderness medicine activities include oversight of clinical research programs to protect U.S. military personnel during sustained, extreme operations, including projects in Rapid Altitude Acclimatization and Immune Hardening. Before joining DARPA, Dr Callahan was principal investigator for the S.E. Asian Polyvalent Antivenin Trial in Na Trang, Vietnam. He maintains disaster medicine billets with two international disaster response organizations.