Okay, so I've secured Spectacle Island. I've build the radio tower. Now I'm supposed to build defenses on the island.

I've built a LOT of turrets, guard posts, etc. But I'm still at 0% complete!

What am I doing wrong (or stupidly missing/misunderstanding)?

Are they assigned to settlers and the turrets hooked up to power(unless the first 2 which don't need it) sometimes the game bugs on settlements and updates randomly for food, defense and such.

I've built defenses other places that didn't need to be manned, like turrets and such. I know that artillery needs to be manned, but this wasn't such a thing. Or am I supposed to build artillery there? I have no idea!