What is the common radar mode used for both military and civil air traffic control?

Mode 3/A is widely recognized as the standard radar mode employed in both military and civil air traffic control contexts. This mode allows ground radar systems to identify aircraft by their transponder codes and to provide basic information about the aircraft's altitude. It is particularly essential for air traffic control operations, as it enhances situational awareness for controllers by displaying the identity of aircraft in a specific airspace along with their tracked altitude.

Using Mode 3/A, controllers can efficiently manage air traffic, ensuring safety and coordination in busy airspace. This mode is designed to facilitate effective communication between the aircraft and the air traffic control system, allowing for accurate tracking and monitoring of flight paths. The simplicity and prevalence of Mode 3/A make it a fundamental component in the operations of both military airspace management and civil aviation.

Other choices, while relevant to radar modes, serve different specific functions or are less universally applied across both military and civil aviation.