[AVGWarhawk]

I did a quick read through on depth keeping and theory, etc. It would seem that the real trouble was not keeping the submarine stable on the horizontal but the vertical, ie rising or decending. It is written that experienced helmsmen did a great job in keeping depth mechanically on the old subs. (therefore, the screaming in Das Boot to watch the depth is not entirely unfounded) Surface wave effects are not experienced the same as a surface vessel. Only under extreme conditions on the surface would the submarine have trouble keeping stable on the horizontal while at periscope depth.

I would leave the stable view checked. Reading about it, I suspect the scope was relatively stable at periscope depth.