Ramming is more riding over the top of a sub and crushing it with the weight of the hull rather than cutting into it. Sort of like breaking ice, you use the hull to break it up not the bow. Not a good idea to plow into a sub by any means and risk the damage.
http://en.wikipedia.org/wiki/The_Enemy_Below
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DID, no cheats, no shortcuts, no non-historic equipment deviations. Boat and crew safety is integral with my immersion style! Follow the historic events during your patrol:
http://www.uboat.net/today.html