What immediate action drill should be performed if the patrol hears or sees an unidentified enemy aircraft?

The appropriate immediate action drill when a patrol hears or sees an unidentified enemy aircraft is to freeze. This action is critical as it allows all team members to quickly assess the situation without drawing attention to themselves through movement or noise. By freezing, the patrol can remain in place and evaluate the threat, gather information about the aircraft, and determine the appropriate course of action without being detected.

In a combat scenario, aircraft may pose significant threats, including airstrikes or reconnaissance, so remaining still ensures that the team minimizes its visibility and potential for detection. This moment of stillness can provide valuable time for the team leader to gather intel and make informed decisions regarding the next steps, whether that involves engaging the threat, seeking cover, or repositioning.

Other options such as a hasty ambush, immediate assault, or return fire may not be suitable responses without properly understanding the enemy's intentions and capabilities. An immediate response can increase the risk to the patrol's safety if the aircraft is merely observing or if the situation is not clearly hostile.