Current standard military vehicle thermal management systems are based on single phase air/liquid cooling. To meet increasingly stringent demands for high power electronics thermal control, two-phase cooling solutions show great potential and can satisfy the need for compact and high heat flux heat acquisition, transport and dissipation under vibration and shock conditions. One novel two-phase cooling technology that has been developed in this work is a new Heat Pipe Loop (HPL), which exploits the advantages of both heat pipes and loop heat pipes while eliminating their shortcomings. Similar to heat pipes and loop heat pipes, the HPL operates on evaporation and condensation of a working fluid and uses capillary forces in the wick for the fluid circulation. Unlike in a heat pipe, the liquid and vapor in the HPL flow in separate passages made from smooth wall tubing. This results in a low pressure drop and consequently great heat transfer capacity and distance over which the heat can be transferred. The evaporator wick in a HPL is also made in-situ through a low cost manufacturing process and has a high thermal conductance, much like the low cost traditional heat pipe wick. To demonstrate the HPL technology, a compact 3kW HPL thermal management system was successfully designed, built and tested in an environment representative of military combat vehicles. This system consisted of six compact plug-and-play HPL modules. Each HPL module was designed to transport 500W of waste heat from two discrete high power devices on an electronics board to a chassis level thermal bus that was a pumped liquid loop. The HPL evaporator (or heat source) temperature was maintained below 80°C with a heat sink temperature of 30-50°C. The advantages of the HPL technology include: (1) Passive operation and high reliability; (2) Low cost in-situ wick fabrication; (3) High conductivity evaporator wicks; (4) Long distance heat transfer capability; and (5) Insensitivity to vibration/shock and gravitational orientation.