Presently, cyber defense heavily relies on human network analysts who must detect and investigate potential suspicious activity, a demanding, fatiguing process that takes a heavy toll on human operators. Given the criticality of these operators to cyber defense, research is needed to investigate and mitigate the sources of those challenges. Currently, few cyber-focused synthetic task environments (STEs) exist, and those that do are not well suited to investigate the problems of network analysts. Therefore, a new cyber STE focused on network analysts called the Air Force Cyber Intruder Alert Testbed (CIAT) was developed. This STE was designed to emulate key functions of Enterprise-level cyber defense platforms. Specifically, CIAT simulates a network analyst environment, including an intrusion detection system, signature database, packet capture software, and network list. The purpose of this paper is to describe the development and validation of the CIAT STE.