[Daniel P. Gross] This paper studies the effects of the USPTO's patent secrecy program in World War II, under which approximately 11,200 U.S. patent applications were issued secrecy orders which halted examination and prohibited inventors from disclosing their inventions or filing in foreign countries in the interests of national security. Secrecy orders were issued most heavily in areas important to the war effort – including radar, electronics, and synthetic materials – and nearly all rescinded en masse at the end of the war.