SunDanzers High efficiency Refrigeration Unit (HERU) technology is a variable speed, two stage refrigeration platform, initially developed under Army SBIR topic A04-210, and continuing with Army Rapid Innovation Funding. HERU currently uses the military standard hydrofluorocarbon R-134a, vehicle type refrigerant. R-134a leaking into the atmosphere has 1400 times the greenhouse gas effect compared to natural refrigerants. The proposed project would retrofit one government supplies MTRCS with a transcritical CO2 refrigeration system while maintaining the capacity and high efficiency of a two stage, variable speed semi-hermetic compressor. The CO2 HeMTRCS will operate in the required dual temperature mode (freezer and refrigerator) at the challenging 135 F ambient condition, where the typical single stage CO2 refrigeration cycle has low efficiency. Poor efficiency leads to greater greenhouse gas production, defeating the purpose of adopting CO2 refrigerant. SunDanzer will supply the proposed demonstration platform as a ruggedized design and at a fieldable readiness level. This evaluation will provide the Army with valuable understanding of the application of CO2 refrigeration to battlefield equipment.