What characteristic is essential for the AIM-9M Sidewinder's operation?

The AIM-9M Sidewinder missile uses a heat-seeking guidance system as its primary mechanism for targeting and engagement. This characteristic allows the missile to lock onto the infrared signatures emitted by the exhaust of enemy aircraft. By detecting the heat, the Sidewinder can effectively home in on its target even in diverse operational environments, making it highly effective in air-to-air combat situations.

Heat-seeking technology is crucial for the AIM-9M's effectiveness, as it enables the missile to track and engage targets without needing radar guidance, which can be vulnerable to countermeasures. This feature allows the missile to maintain stealth and agility during engagements. Other aspects such as dual functionality, GPS navigation, and radar homing are not inherent to the right operation of the AIM-9M, as they pertain to different types of missiles or systems with different operational capabilities. Thus, heat-seeking is the defining characteristic that ensures the AIM-9M Sidewinder can effectively engage and destroy airborne threats.