On the two player co-op mission Overwatch, in the Bravo set of Special Ops missions, it is possible to get this achievement. The player in the AC-130 gunship can get it by shooting the helicopters as they drop men out onto the field, and the player on the ground can get it by picking them off as they rappel down the rope.
Another Special Op mission that you can get this is on Suspension, the final mission in the Alpha set. Part way through the level soldiers will rappel down onto your level from the sides. A quick burst should kill a couple of them, unlocking this achievement.