I'm planning on visiting Nellis AFB for Red Flag 18-2 and Rainbow Canyon area. I'm not sure what focus length is suitable for these two places? The longest I have is 200mm, and I'm thinking about renting a lens.
For the Rainbow Canyon the 400 mm is minimal on the crop body. If you are going to rent 100-400 mm or 150-600 mm lens if you have full frame body you will be fine for both locations.
Red Flag bare minimum would be 400mm. but I wouldn't go there without 500mm. Some birds cut short but a lot go long and then you need every mm from that 500.