The Boeing X-45 unmanned combat air vehicle is a concept demonstrator for a next generation of completely autonomous military aircraft, developed by Boeing's Phantom Works. Manufactured by Boeing Integrated Defense Systems, the X-45 was a part of DARPA's J-UCAS project.

An unmanned combat aerial vehicle (UCAV), also known as a combat drone, fighter drone or battlefield UAV, is an unmanned aerial vehicle (UAV) that is used for intelligence, surveillance, target acquisition, and reconnaissance and carries aircraft ordnance such as missiles, anti-tank guided missiles (ATGMs), and/or bombs in hardpoints for drone strikes. These drones are usually under real-time human control, with varying levels of autonomy. UCAVs are used for reconnaissance, attacking targets and returning to base; unlike kamikaze drones which are only made to explode on impact, or surveillance drones which are only for gathering intelligence.