All of the stock games are pretty forgiving about the deck gun. The biggest issue being that the sub's low profile makes the platform unstable for standard gunnery. The other issue is the damage model. The stock damage model can sink ships with little issue because of the "hit point" model. Realistically (which several mods amongst the games address), it was flooding that sank ships, excluding catastrophic structural damage.
The standard 8.8cm deck gun could do damage, but it required precision shots at the waterline. That was the problem. A lone 8.8cm deck gun trying to sink freighters while fighting its own bob-and-weave in the water was an exercise in frustration and wasted ammo. This is why the manual reserves the gun for light and unarmed ships; to get close enough to get the job done in as few shells as needed.
Likewise, the average surface ship had multiple guns of equal or larger size and a higher, more stable profile to make gunnery a practical choice. Subs are torpedo boats first, ultra-light corvettes a very distant second and only under ideal conditions.
|