The United States biological weapons program officially began in spring 1943 on orders from U.S. president Franklin D. Roosevelt. Research continued following World War II as the U.S. built up a large stockpile of biological agents and weapons. Over the course of its 27-year history, the program weaponized and stockpiled seven bio-agents — Bacillus anthracis (anthrax), Francisella tularensis (tularemia), Brucella spp (brucellosis), Coxiella burnetii (Q-fever), Venezuelan equine encephalitis virus, Botulinum toxin (botulism), and Staphylococcal enterotoxin B. The U.S. also pursued basic research on many more bio-agents. Throughout its history, the U.S. bioweapons program was secret. It was later revealed that laboratory and field testing had been common. The official policy of the United States was first to deter the use of bio-weapons against U.S. forces and secondarily to retaliate if deterrence failed.