A terminal defense is a measure taken against incoming weapons while they are in the terminal guidance phase of their flight, or just the terminal phase: right before impact. This is a difficult task, usually, because weapons will be travelling relatively quickly and may not have any engines firing to produce heat or light to track. On the other hand, they are usually flying towards the defender, neutralizing much of their speed advantage. The Phalanx CIWS is an example of a terminal defense against sea-skimming missiles.