So the point is direct hits on cities tend to have the largest impact because a third - world city is usually not well prepared. (dotearth.blogs.nytimes.com)
To actually unlock them for use you'll have to perform a specific stunt such as getting 10 direct hits with the rocket power to unlock the sticky rocket. (monstervine.com)
It is up to you to count the two consecutive direct hits. (gamecmd.com)