When you sign in with iCloud, your Iron Marine's Invasion progress will be saved automatically. This means that you'll be able to pick up where you left off, even if you uninstall the game or switch phones, as long as you use the same account and have a connection to the cloud.
Before you start
Make sure you have Game Center updated.
- Check for an update going to Settings > General > Software Update
To enable Cloud Save
Open the game and load your save file.
From the map, go to the Settings Menu on the bottom left.
On the top right options, find iCloud and check if the option is enabled.