What key function does a transponder perform during the IFF process?

During the Identification Friend or Foe (IFF) process, a transponder's primary role is to return received signals. It receives interrogation signals from radar systems or other aircraft and responds with a coded signal that contains information about the aircraft's identity. This capability is crucial for distinguishing friendly units from potential threats, especially in military operations, thereby enhancing situational awareness.

The transponder's function is a key part of the IFF system as it provides information that helps prevent friendly fire incidents and ensures coordinated operations in complex environments. While the other functions mentioned, such as acquiring target speed, transmitting data in real-time, and storing previous flight data, may be associated with other systems or components in avionics or surveillance, they do not specifically describe the core function of a transponder in the context of IFF.