Nike-X addressed these concerns by basing its defense on a very fast, short-range missile known as Sprint. Large numbers would be clustered near potential targets, allowing successful interception right up to the few last seconds of the warhead's re-entry. They would operate below the altitude where decoys or explosions had any effect. Nike-X also used a new radar system that could track hundreds of objects at once, allowing salvoes of many Sprints. It would require dozens of missiles to overwhelm the system. Nike-X considered retaining the longer range Zeus missile, and later developed an extended range version known as Zeus EX. It played a secondary role in the Nike-X system, intended primarily for use in areas outside the Sprint protected regions.