[Taqwus]

And a stranger use for an engine-less ship is a star destroyer. Seriously. If you're paranoid and want to build one long before you have a useful target, and you don't want somebody to CI it and demolish your own system, you can just park it away from a star and remove the engines. Then refit and repair them when you're ready to deploy, to minimize the possible Window of Really Unlucky/Stupid Mass Death.

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-- The thing that goes bump in the night