Addressing barriers to widespread Unmanned Aircraft Systems (UAS) operations in the NAS is a key goal of NASA research and development (R&D). One such barrier is the lack of tools enabling operators to team with automation to operate multiple UAS with minimal human oversight. This, in turn, requires a flexible testbed enabling research into key human automation teaming (HAT) areas (e.g., seamless sharing/trading of control between human and automation, trust calibration with highly autonomous systems, transparency, and understanding limitations of automation as a teammate). We propose to develop a ground station that serves as a Human Automation Teaming Testbed for management of Multiple UAS (M-HATT). M-HATT will facilitate R&D into HAT requirements by providing a testbed with: a) an architecture interoperable with NASA's Live Virtual Constructive Distributed Environment (LVC-DE) and international standards (e.g., 4586), and designed with sound properties (modular, flexible, extensible, and scalable); b) tools to configure new experiments without requiring substantial code changes; and c) human-centered interfaces and tools for tuning properties of automation. These capabilities will enable human systems integration (HSI) researchers to rapidly gain insights into challenging HAT research questions. In Phase I, we will define M-HATT requirements and create a proof of concept demonstration. In Phase II, we will implement M-HATT software components, and collaborate with NASA HSI researchers to use M-HATT to perform simulation studies and flight tests, and develop a commercialization plan.