Which IFF modes are exclusively used by the military?

The correct choice identifies IFF (Identification Friend or Foe) modes that are exclusively used by the military, specifically modes 1, 2, and 4.

Mode 1 is used for military purposes to identify a specific class of aircraft, often for strategic or tactical purposes in combat. Mode 2 provides a unique identification code for military aircraft, which enhances operational security and situational awareness during military operations. Mode 4 is a more advanced mode that incorporates encryption, ensuring that only authorized military forces can be recognized as friendly, thus providing a higher level of security against potential threats.

In contrast, Mode 3 is commonly used for civilian aircraft identification, particularly under Air Traffic Control systems. Mode 5, while also military, incorporates advanced capabilities such as better encryption and improved resistance to jamming, but it is not the case that Modes 1, 2, and 4 exclusively refer to military usage in the same way that Mode 3 does for civilian purposes.

This context clarifies why the modes specified in the correct answer align with military use while others have distinct applications that do not pertain solely to military requirements.