[derstosstrupp]

A note to modders/tech-savvy folks: The tvre.org site I linked above in the first post has an example of the slide rule for this method (see part about Auswanderungsverfahren “B”, toward bottom of page). It is relatively self-explanatory how this slide rule is used once you understand the guts of the calculation. Makman had mentioned in a post I’d seen about the desire to implement this slide rule in-game. I second that!

Step 1:
Gain position forward of enemy’s beam. Submerge once a position sufficiently forward of the target’s beam has been achieved. Otherwise, at larger AOBs, approach may not be possible due to the low underwater speed of the sub. Not too far forward, however, that the target presents too sharp of an AOB – your eels will then have little surface area of the target to impact.

Step 2:
Once you’ve nearly closed to firing distance, jot down your own speed (Ve), estimate range to target (E) and note the target’s bearing (b1). Start stopwatch. Do not alter own speed! The rest of this method only takes a couple minutes before firing, and so keep that in mind with respect to “nearly closed to firing distance”.

Step 3:
Once exactly one minute has passed, stop the stopwatch and note the new target bearing (b2). Do not move scope from this bearing until you fire for the rest of the method!

Step 4:
With scope pointed at (b2), set AOB in TDC to 90 starboard or port based on the direction of the target’s bow.

You now have 4 pieces of information noted: own speed (Ve), first bearing (b1), range at first bearing (E) in hectometers (this is important – take your range and divide by 100 and use this figure in the calculations), and second bearing (b2). Remember, this is degrees from the bow, so if she’s at bearing of 330, (b2) for this formula is 30! The change in bearing (b2-b1) we will call (w). Time to crunch numbers (in other words, time for your trusty WO to start spinning those slide rules, and thus pause is fine until you become proficient). Items in parentheses above are used to denote items in the formulas below.

Step 5:
Compute speed for TDC.
1. (Ve) x sin(b2) = (Vk). This represents the speed to input to the TDC IF WE WERE ON A COLLISION COURSE. We are not – the bearing is changing and thus we need to apply a correction:
2. (E) x 3.2967 x sin(w) = (d). Remember to convert your range (E) to hectometers by dividing by 100! The 3.2967 factor is to correct from metric to nautical miles since the correction (d) is in knots.
3. (Vk) +/- (d) = speed to input into TDC. If sub and target bows going in the same direction and the bearing change showed the target pulling ahead, you will ADD correction (d) to (Vk). SUBTRACT if sub and target bows are going the opposite directions, or if you are gaining on target (bows in same direction).

Step 6:
Obtain a final range estimate and input into the TDC (easily estimable since you got (E) already, just use judgment as to what the firing range would now be a minute or so later). After inputting, you should still be on (b2). This is a must to correct for parallax, or the error caused by the fact that you are not shooting torpedoes out of the lens of your periscope, unless of course the gyro angle is within 10 degrees or so of your bow, in which case parallax error is moot. Use whatever your GUI offers. I use Hitman’s top-notch GUI and thus only estimate using the scope reticles. This is more than sufficient. Just know that errors due to inaccurate range will be more pronounced the closer you are and the larger the gyro angle. Alternatively, you could start a turn toward the target once you obtain the gyro angle for the shot and pull the trigger once your bow crosses the zero gyro angle bearing, thus eliminating the need for the torpedo to turn and the need for a range estimate, but I have found this a bit unwieldy in practice.

Step 7:
While still on (b2), toggle TDC to auto, reacquire target and fire! You’re already at a good firing range. That is a benefit of this method – it is very quick once you get the hang of the calcs, all done immediately prior to firing.

There are also other handy uses for the Auswanderungsverfahren method, such as at long distances during the overhaul maneuver to obtain rough speed with a rough idea of target AOB without slowing and thus losing time in overhauling. In time, and if interest is shown by the community, I will post.

Below is a video demonstration of this method:


Enjoy and gute Jagd!