But if informed that an attack is imminent there may be at least one ace up their sleeve.
> A displacement hull won't plane no matter how much power you put into the shafts.
I wouldn't be so sure, the main difference between the two is that a planing hull has an angle of attack in regards to the water, so it can generate lift. You can achieve the same by increasing stern trim on a displacement hull.
As for it being flat on the bottom, there are also less stable flat planning hulls that work so that doesn't disqualify it either.
A Shkval can go as fast as a missile, but it can't turn very well so you might be able to dodge it this way.
Sure it's not a good outlook in any case, but it's better than sitting there waiting to be hit.
... Traveling a few dozen knots faster is an "ace up the sleeve"?
Its a stupid strategy, but it seems to check out. The faster a submarine tries to go, the easier it would be to detect.
Very possibly.
https://en.wikipedia.org/wiki/Mark_48_torpedo
Maximum speed: 55 knots
Effective firing range: 21-27 nautical miles
If your carrier can do anything near 55 knots away from the torpedo, it's safe.