From The TimeSplitters Wiki

The Gunship is the first boss you fight in TimeSplitters 2. You fight it on top of the dam in Siberia in normal and hard mode, and besides escaping through the Time Portal, it is the lat objective of the level. It can shoot a machine gun and rockets at you. The best way to defeat it is with the Gun emplacment, just be careful because some people can run at you while you shoot it. You can basically shoot at it non-stop until it is destroyed.