The UA 571-C Automated Sentry Gun,[1] known colloquially as the Robot Sentry, is a tripod-mounted automated perimeter defense system employed by the United States Colonial Marine Corps to deliver pre-set automatic fire to any hostile within range or area targets. They are equipped with M30 Autocannons and automatic thermal and movement actuated AI targeting capabilities. In 2179, the Colonial Marines on LV-426 used them successfully to keep Xenomorphs from flanking their position while waiting for rescue.