Which military training exercise, starting in 1975, transformed USAF training?

The military training exercise that started in 1975 and transformed USAF training is indeed Red Flag. This exercise was designed to provide realistic combat training for aircrew members in a controlled environment. It simulates the complexities of aerial engagement and includes various elements such as air-to-air combat and ground support missions, allowing pilots and crews to practice their skills against a backdrop that mirrors real-world scenarios.

Red Flag is significant because it introduced a multi-unit training approach, integrating various aircraft, ground support, and intelligence operations. This collaboration enhances teamwork and communication among different units, which is critical during actual combat missions. The training incorporates lessons learned from past conflicts, ensuring that participants are well-prepared for potential future engagements.

The other choices, while they relate to military training exercises, do not have the same historical impact or comprehensive transformation effect on USAF training as Red Flag.