The concept of using variola virus in warfare is an old one. British colonial commanders considered distributing blankets from smallpox victims among Native Americans as a biological weapon.(1-3) During the American Civil War, allegations were made about the use of smallpox as a biological weapon, although there subsequently proved to be no definite evidence for such.(4,5) In the years leading up to and during World War II, the Japanese military explored weaponization of smallpox during the operations of Unit 731 in Mongolia and China.(6,7)