Militarily, the Combine make use of both synthetics, creatures augmented with machinery, and traditional machines such as armored personnel carriers and attack helicopters. The most prominent of the synthetic machines are the insect-like gunships; and Striders, armored creatures that walk upon three legs, which are armed with a high powered warpspace cannon and a head-mounted pulse turret. In "Episode Two", the Hunter, a smaller equivalent to the Strider, is introduced. These 2.5 m (8 ft) tall, tripodal assault machines fire explosive flechettes at targets and are small enough to maneuver indoors. Other synths are seen near the end of the "Half-Life 2", although their roles are not elaborated on. Sentry turrets are also used by the Combine. The Combine also use headcrabs as a biological weapon against dissidents, firing artillery shells loaded with the creatures into areas and allowing them to infest the vicinity.