Shot Blanca was the 35th and penultimate nuclear detonation of Operation Hardtack II, fired on 30 October 1958 in a tunnel at 301 metres depth in Area 12e of the Nevada Test Site — the day before the midnight deadline when the nuclear test moratorium took effect. It was a UCRL test of an alternate W-47 primary in a thermonuclear system mockup, producing 22 kilotons against a predicted 20 kt and declared successful. The W-47 was the warhead designed for the UGM-27 Polaris submarine-launched ballistic missile — the cornerstone of America's sea-based nuclear deterrent. Despite being fired in a sealed tunnel, Blanca vented radioactive material into the atmosphere. The shot was widely reported in the press during the moratorium negotiations of 1959, used to illustrate debates about underground test verification and inspection.