[derstosstrupp]

I will start by answering the specific questions you had. The AOB input is the AOB at the moment you fire, but as has been mentioned, if the TDC is set to update, the AOB will update as you turn your optics, as the bearing changes. So capture an AOB at some particular point that is easy to recognize, and then set the TDC to update and as long as you don’t change course, the AOB should still be correct.

Also, your own speed has no impact on the firing solution itself.

The following are really the “first principles” of shooting, if you want to think of them that way:

1. Speed: The closer your torpedo track is to perpendicular to the target’s course, that is, closer it is to a 90° impact angle, the more speed matters. Speed matters less at lower impact angles, because the speed across the line of sight is lower (lower apparent speed). Generally, at a range of 1000 m or less, you are allowed up to a knot of speed error at a 90° impact angle, up to two knots of error at lower impact angles like 40°. So the takeaway of this is, if you are unsure of target speed, but you are more certain of AOB, try to shoot at a lower impact angle. As always, get close.

2. AOB: By far the easiest to estimate, and error in it has less of an impact on the solution the closer the torpedo track is to 90°. Case in point, at ranges of 1000 m or less, you are allowed up to 10° of AOB error. At lower impact angles this approaches 5°. German doctrine was typically to wait until the target reached 90° AOB before they fired, as it is easiest to estimate by eye. Try to shoot at lower AOBs for higher speed targets. And again, always get close.

3. Range: Here is a huge takeaway, and if you forget everything else in this post, remember this one thing: the lower the gyro angle, that is, the less the torpedo has to turn, the less range matters to the solution. This is true regardless of what the AOB is or what the impact angle is. The calculation for lead angle does not factor in range at all - it is irrelevant as long as the torpedo does not turn. In practice, if the gyro angle is within 20° of your bow, don’t worry about range. The only reason there is a range setting on the computer to begin with is because you are not literally shooting torpedoes out of the lens of your periscope. Instead, the point at which the torpedo gets on course is some 30 m in front of the optics, and so the range setting is needed when the torpedo has to turn like that in order to correct for what is called parallax error. But, if the torpedo does not have to turn, there is no such correction needed, and the range can simply be eyeballed, roughly estimated. In practice, the Germans always strived to minimize the gyro angle for this very reason. And the range was simply eyeballed, normally by how much of the lens the target filled up, definitely not an exact science in practice.

In summary:

1. Get below 1000 m to shoot.

2. Wait til the target presents a 90° AOB as it is easiest to estimate.

3. Strive to get a target speed to within a knot. The easiest way to do this is to simply travel parallel to the target for a while at a long range and match the target’s speed, which was the standard preferred method historically (known as Ausdampfen).

4. To the extent possible, try to shoot when the gyro angle is anywhere from 340° to 20°, that is, within 20° of your bow. This way, you only need to roughly eyeball range, if at all.