Everything in the military is designed to military specifications called 'mil specs' and they represent the standards and design of each piece of equipment used in the US military.
MIL-STD-810 addresses a broad range of environmental conditions that include: low pressure for altitude testing; exposure to high and low temperatures plus temperature shock (both operating and in storage); rain (including wind blown and freezing rain); humidity, fungus, salt fog for rust testing; sand and dust exposure; explosive atmosphere; leakage; acceleration; shock and transport shock; gunfire vibration; and random vibration. The standard describes environmental management and engineering processes that can be of enormous value to generate confidence in the environmental worthiness and overall durability of a system design. The standard contains military acquisition program planning and engineering direction to consider the influences that environmental stresses have on equipment throughout all phases of its service life. The document does not impose design or test specifications. Rather, it describes the environmental tailoring process that results in realistic material designs and test methods based on material system performance requirements