Speed number--figuring out ships speed

[Zosimus]

Originally Posted by Leoz

Great read! Thanks.

Originally Posted by BigWalleye

Some observations:

1. We are at an advantage over our RL counterparts. We know that AI ships only move at speeds in integer knots. Check in the campaign.xxx files. Or turn on the God's eye view so you can get exact data. You'll see what I mean.

2. Knowing the target's speed to better than the nearest integer is not necessary for a successful firing solution. The target is BIG. At 1000 meters, optimum firing range as recommended by KM doctrine, a 140 meter long ship will subtend 8 degrees. The lead angle for a 90 degree shot is 14.5 degrees for a target moving at 10 knots. So if you aim for the center of the target, you can have a speed error of 27% at 1000 meters and still hit. At 2000 meters, quite a long shot, the allowable error drops to 14%. That's 8.5 kts, instead of 10kts. It is not difficult to distinguish between 8.5 and 10 kts.

3. Submarine commanders were warriors, not engineers and certainly not accountants. If you read the first-person accounts, they didn't attempt to determine target parameters with great accuracy, just enough to get the torpedo on the target with a good probability of success. Better to fire two fish, hit, and retire than to try for the perfect shot, get detected, and have to abort the attack. I don't recall ever having read of an RL sub skipper who regarded the attack as a math problem. That's for staff officers.

Remember that the torpedo is a big, powerful weapon. Any hit will do a lot of damage. A heart shot is not needed.

Your argument relies on a lot of bad assumptions.

Let's run with your example. The target covers 8º and we are firing not a center shot but a salvo shot (that's what KM recommended, isn't it?) with a 4º salvo angle that we can control when we switch to salvo mode.

For ease of understanding, we will label the boat thus:

3 2 1 0 1 2 3 (0 is dead center).

So your torpedoes are aimed at -2 and +2

Suddenly your 27% permissible error rate goes out the window. The acceptable error rate must surely fall to 13% or less.

Additionally, you are assuming that the ship is going 10 knots. Most of the convoys I attack are going about 7 or 8 knots. If we re-calculate with 7 knots, and 13% error that means +/- 0.91 knots. That means that if you think the ship is going 7 but it's really going 8, then one of your torpedoes is going to miss.

Furthermore, there's another possible error involved. The speed setting is analog. You cannot digitally enter 7.0 knots. You are moving the dial and it looks like it's 7, but maybe you actually set for 6.9 and you didn't know. Or maybe you tried to set the AOB for 90º at the moment of the shot, but because of inaccuracies, it's actually set to 88º

Finally, perhaps you're right that your average u-boat commander didn't care about the exact math involved. However, if we look at the list of the top 50 u-boat commanders at https://en.wikipedia.org/wiki/List_o...oat_commanders and arbitrarily pick 26 and 27 (about the middle of the most successful pack) we see that they are sinking about 3 ships per patrol and #29 drops to fewer than 2 ships per patrol.

So, basically, your average u-boat captain sucked. And if you do things the way he did, you'll suck too.