[Mr Elusive]

Update:

I fired up the old OLC GUI (v1.2.7) and made a mental note of where the scratch mark was. Lo-and-behold, ValoWay was right - it's just below the 15 marks. I tested the zoomed-out method using ACM Reloaded and it worked perfectly! For anyone interested, these were the exact steps I followed based on OLC's tutorial videos he did:

Finding Range:

1. Line periscope with the waterline of the target.
2. Count the number of vertical marks from the waterline to the highest mast.
3. Find the number of marks on the marks ring.
4. Drag & rotate the marks ring until the value lines up with the "scratch mark" below 15 on the AOB ring.
5. Find mast height on basis ring and use the value it lines up with on the range ring.

Finding AOB:

1. Find mast height value on basis ring.
2. Click & drag to the ship length value on the basis ring.
3. Click & drag from the "scratch mark" so it lines up with 90 degrees on the AOB ring.
4. Count the number of horizontal marks to the from the center to the front of the ship.
5. Find the number of marks on the marks ring and use the value it lines up with on the AOB ring.

I managed to sink a ship on the torpedo tutorial level using this method. Obviously I had to approach a bit closer to the target to do this.

One thing I did discover is that torpedoes have a minimum range of 250m before they arm. If you're engaging ships at that kind of range, you're probably way too close to begin with! So I can kind-of understand why some players never attack while zoomed-out; you're far more likely to get spotted.

Nonetheless, this was a great learning experience for me. Sometimes you gotta experiment or just ask someone who knows.

Thanks a million guys

PS: I will get round to reading that targeting manual at some point.