I'm currently working on a Great War rules set, and here is what I've come up with for the moment.
Whenever a submarine takes damage equal ti or in excess of its hull points, it is "disabled" and suffers the penalties of being crippled. It also is forced to surface, and so can make gunnery attacks and be attacked by guns. Then its hull points reset (though it is still crippled), and it remains in play until the second time it is sunk.
This may need a bit of modification for Hull 2 subs, but I imagine it would work pretty well for the smaller ones.
University Student— Lover of Plato, Aristotle, War At Sea, Palestrina, and Mozart