The first round of Operation Grapple tests was unsuccessful in demonstrating a working hydrogen bomb design. This left plans for Operation Antler in disarray. By mid-June 1957, proposals for Antler included up to seven tests: of a surface-to-air warhead called Blue Fox, a small warhead called Pixie, four different versions of Red Beard, and a round designed to test the principle of radiation implosion. Initially it was planned to test Blue Fox (later renamed Indigo Hammer) in both boosted and unboosted form, but the disappointing results of boosting thus far meant that the benefit of boosting would be too small to warrant it, and this version was discarded. Pixie was an even smaller, lightweight () warhead with a plutonium core under consideration for use with the Royal Navy's Seaslug missile. Its drawback was that it required enough plutonium to build two Red Beards, and plutonium was scarce and expensive. In February 1957, the Australian authorities were notified of plans for six tests, including three using balloons, with maximum yields of up to .