Disclosure forms provided by the authors are available with the full text of this article at NEJM.org. We thank Capt. Ron Schoonover (3rd Medical Battalion), Capt. Maria Young and Cdr. Jackie McDowell (Naval Hospital Guam), Col. William O’Connell (Brian D. Allgood Army Community Hospital), Mr. Donald Brown (Vice President, Maritime Policy with Cruise Lines International Association), Ms. Beth Poitras and Ms. Jessica Newton (Navy and Marine Corps Public Health Center), Cdr. Brian Legendre (Navy Environmental Preventive Medicine Unit 5), and all of those not listed who have responded to this outbreak; Col. James Mancuso (Uniformed Services University of the Health Sciences) and Dr. Art Kellermann (Dean of the School of Medicine at the Uniformed Services University of the Health Sciences), for editorial assistance with an earlier version of the manuscript; and the crew of the U.S.S. Theodore Roosevelt, who despite this unprecedented outbreak, demonstrated resilience in returning to sea and to their mission of protecting our country. The views expressed in this article reflect the results of research conducted by the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of Defense, or the U.S. government. This article was published on November 11, 2020, at NEJM.org. Supplementary Appendix Click here for additional data file. Disclosure Forms Click here for additional data file.