Use at least one grenade, rocket, and air strike in one level to earn this achievement. There are many levels where you can find grenades and rockets. To save some money, just buy an airstrike when you play such a level.
Since weapon drops are random, there is not a specific level I can recommend for this achievement. My advice is to play the game normally, then when you get a level where you pick up a both grenade and a rocket, consider buying an air strike. Preferably do it when there is a large cluster of soldiers you can hit so you can make some progress towards this achievement as well.