Even though the latest version of U.S. Sidewinder air-to-air missile has not completed its testing, the U.S. Navy has ordered 599 of them at a cost of $161,000 each. The new AIM-9X missile is more agile than previous versions and can pick up a target without having to be behind the target. The Sidewinder first entered service in the late 1950s, and has been so successful that no one has been able to come up with a new design to replace it. Thus the seemingly endless improved versions that are able to keep up with the competition.