Since this is merely training, and the "reward" is a few hundred renown points, put the difficulty level to 0%. Once you've completed all the training scenarios, then you can increase your realism settings to whatever you want!
I don't recall the planes shooting at me. dropping bombs or anything else, all the times I went in there just to pass some time. Nor do I remember taking any damage to my sub. That would be like deck gun practice where the targets shoot back and try to sink you.
