What distinguishes Mode 4 of IFF from the other modes?

Mode 4 of the Identification Friend or Foe (IFF) system is distinguished by its use of encrypted communications, specifically designed for military aircraft. This encryption is crucial as it helps ensure secure identification of friendly forces while reducing the risk of interception or spoofing by adversary systems. This secure identification is essential in combat scenarios, where distinguishing between friend and foe can be critical to mission success and safety.

In contrast, the other modes of IFF, like Mode 1, Mode 2, and Mode 3, do not utilize encryption in the same way, making them less secure for military applications. Civilian use of IFF is typically associated with unencrypted modes for air traffic control purposes, which underscores the unique necessity of Mode 4 for military operations where secure and reliable communication is paramount.