In military aircraft, electronics are often subjected to operating environments well beyond their survival temperatures and with limited heat sinks. The current approach is to use a Liquid Cooling System (LCS) with either vehicle fuel or Polyalphaolephin (PAO) to cool electronics. However, advanced military platforms have found this approach limits their operational effectiveness. A thermal management system for electronics cooling in high temperature avionics environments is under development using Loop Heat Pipe (LHP) and heat pipe-based technology. The system reduces thermal energy transport inefficiencies within electronics enclosures, identifies potential sinks to provide continuous heat rejection over the operating envelope of the platform, and provides passive thermal energy transport from the electronics enclosure to selected sinks.The system developed to accomplish these tasks is divided into two subsystems. The first subsystem is responsible for improving thermal transport within the electronics enclosure and consists primarily of heat pipe assemblies. Model results of the first subsystem show considerable improvements over the current implementation. The overall temperature gradient within a generic electronics box decreased from 42.7°C (76.9°F) to 17.8°C (32.0°F), increasing the allowable sink temperature from 66.7°C (152.1°F) to 91.7°C (197.1°F). This increase allows for more freedom in sink selection, which is typically limited aboard military platforms. The second subsystem transports thermal energy from the external surface of the enclosure to appropriate sinks and consists primarily of a LHP. At this stage, several sinks have been identified and evaluated. Final sink selection is underway. Depending on sink temperature and capacity throughout the operating envelope of the platform, multiple sinks may be used. During operation, the LHP will passively select the appropriate sink.