What is the main function of the MK-124 during daytime operations?

The MK-124 is primarily used during daytime operations to signal with smoke. Its design includes a pyrotechnic device that produces a dense orange smoke when ignited, making it highly visible in daylight conditions. This characteristic allows personnel to communicate their location or provide a distress signal effectively in situations where other forms of signaling may not be as visible or effective.

In contrast to the options about illumination, distress signaling, or navigation, the MK-124's smoke signal is specifically tailored for daytime use, which is why it is the correct choice. Illumination is not effective during the day due to the brightness of sunlight, and while the MK-124 can indeed serve as a distress signal, its primary function in this context is the production of smoke to ensure visibility over distances. Additionally, it does not serve the purpose of navigation, which involves determining one's position rather than signaling for help or visibility.