You only spawn shields after the ship has been placed in its starting position. From hence forward the ship should only be moved with the magic ruler.

I'm still playing with this, but found a few things; spawning shields after placing a saved fleet resulted in a error for me. 'Attempt to index a nil value'. When I pull a newly spawned ship from a fresh card (not saved) it works fine.

Nevermind, was reading the instructions incorrectly, and had saved with spawned ships. Should spawn with the descripton after placing the saved fleet.