Operation HARDTACK II Nuclear Events, 1958 (Continued) Event Date Type Yield (kilotons) LOGAN 16 October Tunnel 5 DONA ANA 16 October Balloon 0.037 RIO ARRIBA 18 October Tower 0.090 SOCORRO 22 October Balloon 6 WRANGELL 22 October Balloon 0.115 RUSHMORE 22 October Balloon 0.188 SANFORD 26 October Balloon 4.9 DE BACA 26 October Balloon 2.2 EVANS 29 October Tunnel 0.055 MAZAMA 29 October Tower NMY* HUMBOLDT 29 October Tower 0.0078 SANTA FE 30 October Balloon 1.3 BLANCA 30 October Tunnel 22 *No measurable yield 4.17.1 Background and Objectives of Operation HARDTACK II. HARDTACK II was the last nuclear test series before the United States adopted a nuclear test moratorium, which had originally been intended to last 1 year but continued until 1961. The nuclear weapons tests were conducted to evaluate the yield and efficiency of newly developed nuclear devices (21: 1,7). Concern about nuclear weapon proliferation intensified throughout the 1950s, particularly after the BRAVO test of Operation CASTLE and the heavy fallout resulting from this shot. India proposed a cessation of tests. At that time, Prime Minister Nehru of The call for a test ban figured repeatedly in disarmament discussions, most importantly, those of the Disarmament Subcommittee of the U.N. Disarmament Commission, 18 March to 6 September 1957. in session from Continuing pressure on the nuclear powers to reach an agreement on limiting testing resulted in the Conference on 126