Attack Drones are light, fast swarms that hunt and kill enemy defense structures. Weak vs Anti-air defenses and enemy infantry; Strong vs ground targets
Attack Drones are the first air unit you acquire in the game. These drones can fly over and ignore obstacles on the map such as walls and rock walls. Attack Drones cannot be attacked by some base defenses such as the Guard Tower, Artillery, Spider Drones, and tanks. Additionally, as a flying unit, it will ignore any enemy forces that do not attack it and go straight for enemy buildings. Because of their speed, attack power and potential to swarm, Attack Drones can quickly decimate enemy bases if they have no air defense. The weakness of this unit is that it is very fragile and does very poorly against anything that can shoot up into the air.
Weaknesses:
Patriots do area of effect damage on flying units. A few attacks from these can reduce a fleet of drones to dust.
Domed Aerial Defenses and the Standard Dome Turrets also deal fair amounts of damage to drones (with the specialized aerial defense being able to engage multiple turrets simultaneously).
Enemy Infantry can obliterate drones if left unattended.
Enemy Stealth tanks are notorious for stopping entire fleets of drones by chaining their EMP attacks. Watch out for any bases devoid of visible troops (or left without adequate troops) - it more than likely implies Stealth Tank squadrons lurking to counter-attack.
Strengths:
Enemy Guard Towers, Artillery Batteries, THELs, Metal Rains, Rail Guns, MLRS Launchers, Tanks, Spider Drones all have one thing in common. They get blown up by Drones, and they can't do anything about it.
Drones have extremely high speed (movement and turn), so moving around the map between targets is not a problem for them. They also have moderately high damage per unit (very good damage in squads
Drones prioritize defense structures over everything else. Make sure to take out anti-air defenses, because once these drones are let loose, they can obliterate an entire base in a flash.
They will engage ground units such as infantry that attack them. They will also target Tanks and Spider Drones if they are engaging your ground forces, so deploy them strategically.
Strategy:
It's always good to have at least one tarmac for drones. At the worst, they can be assigned clean-up duty after killing most of the base (to secure the 100% base destruction bonus. They can also be used to take out isolated defense structures, while the rest of the troops head in a different direction towards the rest of the enemy base.
Sometimes, you can use a full fleet of drones (on all the tarmacs) if you're confident that you can take out all their air defenses before-hand. This can lead to quick victories with minimal casualties. Beware though - drones die as fast as they kill. Since they are moderately expensive in comparison to other units, a single failed attack can have big consequences in terms of wasted fuel.
Drones are most often best used as a partial strike force (2-3 dedicated tarmacs). By using the ground troops to mop up initial air defenses, you can deploy an EMP before using the drones to mop up some remaining air defense structures first, before killing the rest of the ground-defenses.
If the enemy has too many air-defenses, it may best not to use any drones for the battle. They have a fairly quick deploy time (1-2 minutes for the full tarmac) -> so redeploying them for the next battle is a small task.
Speed boosts and Heals are critical for drones and can help preserve drone hitpoints during the midst of a climactic battle. Theses boosts can many a times, dictate the outcome of a drone-centric battle.
No matter how vigilant you are, sometimes, those pesky Stealth Tanks can cripple the fleet. By deploying or directing Rangers or Stealth Tanks, you can free up the drones to go back to killing enemy structures. By contrast, drones don't have particular synergy with most other ground units (other than the fact that they can destroy ground-based defenses to clear the way).
Drones can have really good synergy with Apache's (the Aerial Tanks). Apache's can be used to soak up damage from anti-air defenses before drones swoop in for the kill.
Stealth Tanks can be deployed strategically (using the single deploy method) to freeze anti-air defenses, allowing drones full reign over the battlefield.
Drones can be used to store fuel overnight (or when you're not playing, due to the fact that they cost alot). In the morning, you can convert them to some other troops and get the fuel back.
Trivia:
A single Stealth Tank can freeze a large number of drones by chaining the EMP burst.
Friendly EMPs can freeze your own attack drones - be mindful to drop the EMP BEFORE directing the drones to the targeted area.