A system-level thermal modeling methodology for shipboard power-electronics cabinets is presented and demonstrated for a PCM-1 cabinet, a complex air-to-water-cooled cabinet design of interest to naval applications. The cabinet is completely sealed and the heat dissipation in the power electronics bays is removed from the cabinet by re-circulating the hot air through an air-to-water-cooled packaged heat exchanger that is served by an external fresh water loop. A detailed unit-wise analytical model is developed for the packaged heat exchanger used in the cabinet. Under the prescribed design parameters, the PCM-1 cabinet operating-point air circulation rate was established to be 0.434 m3/s (920 CFM). A compact model is developed for the air convection within the cabinet using 3-D Computational Fluid Dynamics/Heat Transfer (CFD/HT) simulations in conjunction with Proper Orthogonal Decomposition (POD)-based reduced order modeling techniques. The compact model runs about 350 times faster with a mean prediction error within 3.6% for the velocity field, 0.04% for the temperature field, and 0.15% for the pressure field. The resulting overall cabinet model can be integrated into a system-level modeling platform to simulate the thermal response of multiple cabinets. The CFD/HT simulations of the PCM-1 cabinet architecture suggest that its two uppermost bays would experience high air temperatures due to insufficient local air flow.