The problem with Battleships....
They have heavily armored sides and anti-torpedo bulges and bulkheads and whatnot, especially the WWI era BBs like the Revenges...
the lesson here, as the Americans did against Yamato and the British against Bismarck is to aim forn the bow and the stern since those are not heavily armored.
If you're going for the mag-shots in 1939 though there is the malfunction problem of torpedoes running too deep. the normal correct depth is between 1 and 1,5 meters below draft, which in your case means nearly on the bottom, malfunction or early detonation because of hitting the seeabed almost guaranteed.
to compensate for this, set the depth to 7.5 meters, if it does run correctly though it will almost certainly bounce off the ship and misfire
Since you're only going to get one shot and you want to maximize damage, what I'd do is aim an impact 3 meters depth at or near the bow, another at the stern and aim 1 mag set to 9 meters (or 10 if heavy weather) at the B turret (second from the bow) if you fire a fourth make it a mag aimed directly for or between the smokestacks. Do NOT fire impact eels at the armoured sides of a Battleship, chances are you won't sink it.
In the cases of Battlecruisers however, aim impact eels set to 4 meters at the A turret, between the smokestacks and C turret. I took out HMS Hood that way, cracked her right in two...
you've got yourself into a sticky situation, best of luck to you
