Yeah, it’s confusing. The control you have is the shield enable/disable button.
This is incorrect.
If your shield is enabled, the bubble will go up after a certain number of your troops, including troops on primarchs and castle guards, have been killed. Only the owning team’s troops count. Once your bubble has been triggered, it will last for a certain time if you do nothing. You can drop it early by disabling the shield. Whether you drop early or let it expire naturally, you then enter cooldown, which lasts a fixed duration based on castle tier. Anyone can see the shield status in the Fort. If the shield is enabled, that includes troops to bubble, time remaining on bubble, or time remaining on cooldown.
For a tier 2 castle, it’s 80k troops killed, default duration of 24 hours, and cooldown duration of 3 hours.
Things to do:
- Disable the shield to prevent getting bubbled if you think you can fight your attackers off. If you change your mind, you can always reenable and let it bubble as long as you can get 80k (or however many) of your troops there to die.
- After you get bubbled, try to drop early at a time when you and your allies can defend and a time that’s inconvenient for your enemies. Some people like to leave it disabled during cooldown so opponents can’t see that it’s in cooldown or how much time is left.
- Remember to re-enable the shield after disabling. It won’t go back on by itself.
Here’s a PG reference