Taking these factors into consideration, ARPA outlined four potential approaches to a new ABM system. The first was Nike Zeus in its current form. The second was Zeus combined with a new radar system. The third included new radars and computers. Finally, the fourth, or X, plan called for all of these changes, as well as a new short-range missile. As the shorter range missile would overlap with Zeus, X also called for Zeus to be modified for even greater range as "Zeus EX". After considerable debate, the decision was made to cancel the existing Zeus deployment and move ahead with the X plan.
