January1, 2007: The Pakistani Air Force is paying an American firm about $19,000 each to have 310 AIM-9M Sidewinder air-to-air missiles upgraded to the AIM-9M8/9 standard. This involves minor improvements in the electronics and rocket motor. In most air forces, air-to-air missiles are never fired, but end up exceeding their shelf-life and being taken out of service then, or when they otherwise become obsolete. In this case, a missile that is still considered quite effective, is being given a check-up and minor upgrade, to make them useful for another 5-10 years. The missiles will be refurbished in the United States. This project is part of a larger, $5.1 billion effort to add 36 F-16s to the Pakistani air force, and upgrade existing aircraft, and associated equipment and weapons.