[Penelope_Grey]

1) unsure

2) with great difficulty, there is no night vision option just like the old days, no, you just have to squint or take your best guess especially if using manual torpedoing.

3) I think, personally speaking the most efficient way is to shoot 4 torpedoes into it.
The first torpedo aim for the forward magazine of the battleship which is located roughly under the forward turret, set the torpedo to run about half way between the waterline and the keel for impact settings.

the other 3 torpedoes shoot in a salvo quickly after the first torpedo to pulverise as many compartments as you can to create optimal flooding situations and the darn thing should sink like a brick.

4) Not that I am aware of, I am fairly certain that all torpedo warhead yields are the same.

5) With the GWX in so far as upgrading the engine is concerned, the team pretty much null and voided this a bit, in stock game a MAN VIIC could do 20 knots on a calm sea flat out, the best possible they could do was 18 at most that was the sheer death of it. All U-boats when built had supercharging to get as much speed out of the diesels as possible.

GWX models it in such a way, I believe if I am remembering right from what Kpt. Lehmann said... is that tehy powered down the non-upgraded engine slightly only very very slightly, and the upgrades they decreased the significance of, so that the U-boats would not go excessively faster than their historical top speeds. If that makes any sense.

So when you upgrade to a MAN engine, you are in fact just upgrading the U-boat to its historic top speed, which on a VIIC is about 18 knots going flank. But in reality, the differences in GWX are now very very slight.