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Such torpedoes would be small enough that you could easily fit dozens of them in a frigate (which already has torpedo tubes, for disruptor torpedoes), considering a ME frigate is around as big as a modern battlecruiser.
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If this became a battle of missile boats then it would be trivial for anyone of note in Mass Effect to build torpedoes with similar-to-higher yields and much better acceleration (their ICBM equivalents can pull hundreds of gees, so deci-gees for smaller missiles really shouldn't be unreasonable here). Even assuming that they are megaton weapons (which, if you can scale the diameter/depth ratio of an asteroid crater to that of one on Earth, they're not) they're very slow. can't see the Citadel powers (or the Terminus ones, for that matter) being too impressed by these.
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