The american subs were pretty quick in getting under some reading I've done suggests around 30-50 seconds for a dive. My reading also suggests it took a lot longer to surface, mostly on perpose to stop hull poping. And yes a boat could dive and surface with out forward speed. It took a lot of compressed air and was noisy but it could be done.
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Ultima ratio regum. (The final argument of kings)
- Inscription on french cannons, on order of Louis XIV
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