On July 15, 1966, 18 U.S. senators sign a statement calling on North Vietnam to “refrain from any act of vengeance against American airmen.” The number of captured American pilots was on the increase due to the intensification of Operation Rolling Thunder, the U.S. bombing campaign against North Vietnam that served as a core element of President Lyndon B. Johnson’s Vietnam policy. The lawmakers’ statement reinforced the message of a cablegram sent to North Vietnamese President Ho Chi Minh on behalf of American captives, penned by the National Committee for a Sane Nuclear Policy (SANE). The group included prominent anti-war activists such as Dr. Benjamin Spock, socialist Norman Thomas and Harvard historian H. Stuart Hughes. On July 16, the United Nations Secretary General also urged North Vietnam to exercise restraint in the treatment of American prisoners of war. Three days later, North Vietnamese ambassadors in Beijing and Prague asserted that the captured Americans would go on trial as war criminals. However, Ho Chi Minh subsequently gave assurances of a humanitarian policy toward the prisoners—in response, he said, to the appeal he received from SANE. Despite Ho’s assurances, the American POWs were routinely mistreated and tortured. They were released in 1973 as part of the provisions of the Paris Peace Accords that were signed on January 27, 1973.