Landing on Moon after enemy has control?

Ok I was playing a single player game and the enemy general landed on the moon without me knowing. Once I was able to get to moon. He had so many flying units, every time I tried to land anywhere on entire moon they died instantly by air attack. The game had to be canceled for there was no way to defeat the enemy. There needs to always be away to counter anything and not have it based on luck of whatever tech you unlock. I even launched 20 ships with anti air and they couldn't hold the area he has so many air units. It was a no win situation and the last guy ti beat to win galaxy map.....sigh

20 is NOTHING. You need at least 100. What I did was spam Vanguards 100 at a time and plop them on top of the base in the vain hope of being somewhat near the enemy commander.

It's easy, just use some unit cannons to fire at different locations on the planet and overwhelm them with anti-air and advanced units... wait...
Nope, still can't do that.

Send an engineer out into the asteroid belt, covertly construct some Halleys, (implying you have Halley tech) and enjoy planetary bumper-cars... wait a minute...

Just make enough transports to crash your computer and use area commands to send a million units at .01 fps at their planet, go and eat dinner or something, come back in a few hours and watch your giant army get shredded by bombers and fighters before it even lands.
Amazingly enough, people are okay with this being the only viable option.

I tried to drop 1000 but the game crashed lol

This is *only* a problem in the GW due to restricted tech. In the main game you can:
1: Planet smash
2: use transports as you said
3: Use anchors to rain death from above
4: Use orbital fabbers to build a gate and bring in literally hundreds of units ready and waiting at a pre built gate on your planet (note for option 4, you require anchors above possibly after sending in orbital fighters to clear an area)
5: Nuke em'

Now this is an issue in GW as you don't necessarily have all those tech options. On the other hand, same thing applies on land "oh I could just use boom bots to clear, oh don't have those"...

You can also:

6: SXX snipe

The AI is particularly vulnerable to this as well.

A player I played with put it very accurately... Related to real world warfare. You have to d-day that planet. You have to d-day the CRAP out of it. Lots of transports loaded with different units. You'll want some tanks and a large amount of AA landing for sure, along with a handful of engineers. The combat units are to protect your engineers long enough to get a teleportation gate up and to then start streaming units through it from your home world.

Precisely! It isn't meant to be easy. Add some anchors overhead into that mix your onto a winner

Well all my transports died before they can even drop units, no matter how many I send. Oh well it will get worked out as the game gets worked on. Thanks everyone for the info

Actually, you're in luck!

LOL but relly easy way - spam Archos make a hole spawn a teleport as bate let the archors kill the air units then invade

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With basic orbital tech you can use orbital fabricators very quickly, and with 9750 health, they are pretty tanky. Don't just build one, either, build several, and rush through with some spinners and other units. Include fabricators so you can pop up whatever defensive structures you might want.