Which of the following is NOT a method to reduce thermal stress on a weapon?

Mechanical cooling is not typically classified as a method for reducing thermal stress on a weapon in the context of thermal management techniques. Instead, it generally refers to methods requiring active mechanical means, which may not be feasible or practical for most weapons systems.

On the other hand, radiational, conduction, and convection cooling all involve passive or natural methods of heat transfer that can effectively manage and disperse heat build-up in a weapon system. Radiational cooling adheres to the principle of heat dissipation from the weapon through radiation, allowing it to lose heat to the surrounding environment. Conduction cooling involves heat transfer through solid materials, where heat flows from the hotter parts of the weapon to cooler parts, helping to evenly distribute thermal energy. Convection cooling relies on the movement of air or fluids around the weapon to carry away heat, which can be particularly effective if the weapon is in a dynamic environment.

These methods are integral for maintaining operational effectiveness, preventing overheating, and thereby ensuring weapon reliability and performance.