This achievement requires you to complete the game first on Perfect Agent difficulty in either solo or co-op. Once you have unlocked Dark Agent difficulty load up any level you prefer (except mission 13, boss fight since that mission doesn't count).
I chose mission 0 since the beginning half is a tutorial and can be run straight through. The only problem you'll have is the last part of the mission when you need to get to the rocket. Take it slow as you make your way to the launch pad elevator. Once on the elevator and the jetpack guys start attacking aim for their head as best you can. As you take out 2-3 jetpacks move towards the rocket door and the mission will end. Upon pressing mission select or next mission the achievement will unlock.