Designed by Ben Lexcen, built by Stephan Ward, owned by Alan Bond and helmed by John Bertrand, the Australia II featured an innovative winged keel design developed by Lexcen. This helped to make it very fast and manoeuvrable in many conditions, and was the most notable and controversial design feature of the boat. During the summer of 1983, as selection trials took place for the Cup defence that autumn, it was unclear whether the keel design was legal within the strict rules governing the 12-metre class.

Questions also surrounded the Dutch involvement in the design of the keel, which under the rules had to be designed by an Australian. The keel design was eventually confirmed as legal while the keel origin controversy remains unanswered. Despite being the first 12-metre to sport the new design, Australia II was not the first boat to have a winged keel, though her success did much to make the concept popular.