[2021] died in a GK in 3 minutes to enemies I can't fight.

I'm curious to know how a submarine got in range within 3 minutes?
I play GK a lot - and to deal with a determined CV you need to stay near another ship with decent AA to prevent multiple passes on you from the same air group. It's not a sure-fire thing always, but it's better than being alone.
Don't be afraid to hang back a bit in your GK at the start. You still have 19km guns at the bare minimum so trade at range until an opportunity to get aggressive and push opens up.