quite unrealistic i should think.
i think in real life, the DD would have likely suffered some damage... perhaps even moderate damage and manageable flooding.
however in the process it would have sliced through your U-boat like chainsaw through a stick of warm butter.
You're boat would have probably been so severely damaged that it would need to be abandoned... or it would have simply sunk altogether.
think of the mass and inertia.
assuming the DD was lining up for a Depth Charge run, he would have been moving about 2500 tons at speeds upwards of 30+ knots.
that would have completely steam rolled over the 800(ish) ton U-boat which was probably moving at 4 knots or less.
the effect this would have had on your boat would have been catastrophic and irrecoverable to say the least.
i would estimate roughly - that perhaps 10-20% of your crew would have been killed in the immediate collision, about that percentage again would have suffered serious injuries some of which would have rendered many of them more or less useless for activity of any sort.
the boat... much of the conning tower would have likely been crushed causing immediate flooding in the control room at a rate of several thousand gallons per minute.
such damage probably would have been almost universal from the conning tower forward.
the aft compartments probably would have emerged mostly unscathed.
the boat would pretty much be a total loss.
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