The Troop Tarmac can produce any of the units that are available. Try to have the maximum amount of troops for your level built at all times. This will allow you to deploy a variety of units when you launch attacks. Upgrading a Troop Tarmac allows it to hold more of any type of unit at the same time. You can also spend gold to speed your troop production by tapping the lightning bolt icon at the side of the screen. After your HQ has been upgraded to level 4, you will have the ability to place troops one at a time instead of in entire squads. This is very useful when attacking a base for the first time, and allows you to try various tactics without committing an entire squad. To toggle between squad and single unit deployment, tap on your HQ, then on the helicopter icon that appears on the menu at the bottom.