of atmospheric, surface-level, and underwater nuclear tests. Eisenhower instead insisted that any moratorium be linked to reduced production of nuclear weapons. In April 1958, the US began Operation Hardtack I as planned. The Soviet declaration concerned the British government, which feared that the moratorium might lead to a test ban before its own testing program was completed. Following the Soviet declaration, Eisenhower called for an international meeting of experts to determine proper control and verification measures—an idea first proposed by British Foreign Secretary Selwyn Lloyd. The advocacy of PSAC, including that of its chairmen James Rhyne Killian and George Kistiakowsky, was a key factor in Eisenhower's eventual decision to initiate test-ban negotiations in 1958. In the spring of 1958, chairman Killian and the PSAC staff (namely Hans Bethe and Isidor Isaac Rabi) undertook a review of US test-ban policy, determining that a successful system for detecting underground tests could be created. At the recommendation of Dulles (who had recently come to support a test ban), the review prompted Eisenhower to propose technical negotiations with the Soviet Union, effectively detaching test-ban negotiations from negotiations over a halt to nuclear weapons production (the one-time US demand). In explaining the policy shift, Eisenhower privately said that continued resistance to a test ban would leave the US in a state of "moral isolation." On 8 April 1958, still resisting Khrushchev's call for a moratorium, Eisenhower invited the Soviet Union to join these technical negotiations in the form of a conference on the technical aspects of a test-ban, specifically the technical details of ensuring compliance with a ban. The proposal was, to a degree, a concession to the Soviet Union, as a test ban would be explored independent of the previously demanded cutoff in fissionable-material production. Khrushchev initially declined the invitation, but eventually agreed "in spite of the serious doubts" he had after Eisenhower suggested a technical agreement on verification would be a precursor to a test ban. On 1 July 1958, responding to Eisenhower's call, the nuclear powers convened the Conference of Experts in Geneva, aimed at studying means of detecting nuclear tests. The conference included scientists from the US, Britain, the Soviet Union, Canada, Czechoslovakia, France, Poland, and Romania. The US delegation was led by James Fisk, a member of PSAC, the Soviets by Evgenii Fedorov, and the British delegation by William Penney, who had led the British delegation to the Manhattan Project.