[Spaceships] Orion space drive: launch from underwater?

[Agemegos]

Originally Posted by Flyndaran

Not rocket-torpedo-lifter stage launching the whole thing to the surface?

I don't see an advantage in engineering it that way. Buoyancy is cheap and simple, and has enormous thrust with terrific endurance.

Exactly how deep does this vehicle start from?

I'm hoping not to have to be specific about that. In a superscience setting it might have to be a couple of klicks deep for the greeblies' civilisation not to have been detected by "scanners". In any setting in which the sci fi is as hard as flan or harder the greeblies will have their civilisation in the photic zone of depths and will build their spaceship on top of an isolated seamount, but orbital sensors won't be able to casually scan the oceans and find the ship and launcher.