The Unmanned Underwater Vehicles (UUV) designed for the detection and neutralization of naval mines are characterized by their high requirements regarding the reduction of the signatures of a vessel (thermal, acoustic, magnetic, etc.), all of them must be reduced in order not to be detected by the mines during the mission. This research work focuses on the reduction of the thermal signature transmitted by the UUV hull, where the use of phase change materials (PCM) is proposed as thermal insulation, placing it between the internal heat source of the UUV and the pressure hull, with the aim of drastically increasing the time in which the external face of the hull of the UUV is within a range of 3 °C and 5 °C temperature increase, allowing it to perform its mission without being detected by the thermal sensors of current naval mines. The simulation will be carried out using the Network Simulation Method for the resolution of the governing equations, which will allow the optimization of the necessary insulation thickness according to the required mission profile. In addition, it is proposed an expression that relates the PCM thickness and the time needed to reach a certain temperature increase.