A submarine can be lost through environmental conditions or a relatively small mistake with far fewer recovery options than a surface ship offers. That does not diminish submarines' military value, but it makes an all-submarine fleet a risky simplification. Submariners accept unusual danger even in ordinary service.
Notable Point · 3:18:42-3:19:34
Why submarines are not a complete fleet answer
The physical danger of underwater operations is used to challenge claims that future navies should consist only of submarines.