Stassen's failure in London proved to be only a temporary halt in the march to test ban negotiations. On March 31, 1958, only days after they had campleted their most extensive series to that date, the Soviet Union announced a unilateral test ban and appealed to other nuclear powers to halt their tests. President Eisenhower and Chairman Nikita Khrushchev agreed shortly thereafter to sponsor a technical conference to determine whether a system to detect nuclear weapontests could be created. August The technical conference was held in Geneva from July 2 wtil 21, feasible. 1958, and concluded that such a system was technically President Eisenhower accepted the conclusions of the con- ference and announced on August 22 that the United States would suspend testing for a year once test ban negotiations began. 42 With a test ban at hand the Commission tested at an even more urgent pace. Phase I of the Hardtack series, held at the Pacific proving grounds from April through August 1958, consisted of thirty-five shots, most of them relatively small. Rockets carried two megaton renge experiments high into the atmosphere from launching sites on Johnson Island. Phase II of Hardtack, held at Nevada, consisted of nineteen shots, four of them underground and ten with the devices suspended 1900 feet above the ground by balloons. fallout was minimal.“* 1958. Most of these shots were small anc 42 © The Hardtack series concluded on October 30, On November 1 test ban negotiations opened in Geneva. “For a time, the era of confrontation between the United States and the Soviet (& Union was giving way to an era of negotiations.