sea mode worked great, you had to adjust for the relative movement of the target (ie. leading like deflection shooting in aircraft). it was essentially like the directors used by most ships for most of WWII (unlike the completely unrealistic, ultra-modern radar guided system used by puffy ack ...). it took practice to get good at.
Yeah, but don't you have to set the same lead every time you fire?
Ok, I've done work on simulations before, like the Dreadnought Project website where the guy simulated a Dreyer fire control table. I've also done manual Torpedo Data Computer aiming in Silent Hunter games. Yes, I am one who likes that sort of thing.
You set range, speed, bearing, and course of the enemy, then adjust the numbers over time as you never get them right the first try. Ships have mechanical computers (about as big as a fridge) that have knobs you turn on them for those settings, and they give you a running solution to lead the enemy, and that is how the turrets are aimed.
1. Range. Use a Range finder. Those boxes on top of the ship are two horizontal periscopes with finely adjustable prisms. You create a right angle geometry solution with it (they do the math for you, don't worry). Bassically you see two images from each side of the range finder, then turn a knob to line them up so you only see one image. That gives you the range. Or you can go vertical with a stadimeter from the waterline to the top of the mast, but that requires you to know how tall the thing you are looking at is (you use a book made up before the war with every known ship in it).
They also have radar, which makes using the periscope system just a backup.
2. Bearing. Easy. Which way was the range finder pointed when you looked at it?
3. Course. Harder to figure out. Takes time. You can guess the first time based on what direction the enemy looks like is going. However, after having made several plots on a map sheet on the enemy ship with the range finder you can see his course that way.
4. Speed. Again, takes time. You guess at first, but after having plotted the enemy down on a map several times, preferably 3:15 minutes apart, you can figure out the speed. I say doing a plot every 3 minutes and 15 seconds is best, as you won't need to do math. Just measure the distance traveled in that time. If the guy moved 1500 yards/meters in that time, then he is going 15 knots. This might be redundant in AH as all ships go 35 knots no mater what.