What IFF mode is used to identify a specific unit?

Mode 2 is specifically designed to identify a specific unit or military aircraft. This mode allows for the transmission of a unique four-digit identification code that is assigned to an individual aircraft. When an aircraft operates in Mode 2, it increases the capability of ground-based radar systems and friendly aircraft to positively identify and differentiate their own units from potential threats.

Mode 1 often provides general identification and does not specify a single aircraft. Mode 3/A is typically used for air traffic control and identifies civil and military aircraft without a direct link to specific units. Mode C adds altitude reporting functionality to the identification process but does not focus solely on identifying individual units as Mode 2 does. Thus, when identifying specific units, Mode 2 is the most appropriate choice.