Actually, R gives one type of rocket only. Press the right mouse button for switching between weapons. The one shooting multiple missiles is almost a granted hit when successfully targeting enemies.

and pull mouse up to ascend

I choose the rocket 2 because the reload time is quicker.
And also since the aircraft control is like a drunken skunk, don't fly too low and don't move your mouse to the left or right.
I need 3 attempts to actually finish this mission