Which of the following is part of what military flights must communicate when changing from VFR to IFR?

When military flights transition from Visual Flight Rules (VFR) to Instrument Flight Rules (IFR), it is essential for them to communicate their position and time to air traffic control. This information allows controllers to maintain situational awareness and to manage traffic effectively, especially in busy airspace where both VFR and IFR operations might be occurring simultaneously. Providing both position and time helps to ensure that the controller can understand where the aircraft is located at that moment and when it plans to reach specific points, facilitating a safe and efficient handoff into the IFR environment.

Factors like fuel efficiency, altitude only, and weather conditions, while important in overall flight planning and safety, do not specifically form part of the mandatory communication required when changing from VFR to IFR. Communicating position and time is a critical aspect of ensuring that all aircraft operate safely in the controlled airspace.