S boats and Mark 10 Torpedos

[ColonelSandersLite]

Hey, first post here with a few questions

Been playing an s-boat campaign (full switch)

I've been informed that the S-boats did not ever have TDCs fitted to them. Is this information accurate?

If S-boats did not have TDCs, was there a means of setting a torpedo gyro angle manually or where they strictly straight run?

Supposing that you're in a newer sub, say a tambor equipped with mark 10 torpedoes, would they work with the TDC there?

I've hunted around for information on this, but frankly trying to find information on the mark 10 is much harder than finding information on a mark 14.

Strangely, it seems it's also easier to find information on German s-boots than it is to find information on the s class submarine.


Anyways, been having fun restricting myself to 0 bearing shots without the tdc. Seriously useful skill to have.

[SteamWake]

First time Ive heard this it may be true.

I dont know how you would hit anything without a TDC.

It is true though that most early torpedoes had to have their gyros set BEFORE they were put in the tube. The game kind of glosses over that fact.

[ColonelSandersLite]

A 0 bearing shot without the tdc isn't that difficult to do really, and even has a hidden advantage or 2.

Basically:

Run your plot normally, and pick the point along the target path that you will kill him (hopefully!).

Point the submarine at that point. Your 0 (or 180 bearing for stern tubes on later model subs) has to intersect his track at the desired impact point.

Determine torpedo run time in seconds, which means you need the distance between your sub and the impact point in addition to torpedo speed. The formula (imperial not metric) is:


Run time = range to impact point / (torpedo speed * 0.5625)


Determine the distance the target will go in that time. Formula (again imperial not metric):


Target Travel = Target Speed * 0.5626 * Run time


On your plot, the aiming point is where your target will be when you fire. Simply use the circlular distance tool centered on the impact point measured out to the target travel distance above, and that's the right spot.


Measure the angle between the impact point and the aiming point.

Point the periscope at the aiming point. (don't forget to send a 0 bearing if you've been using the stadimeter or your torpedoes will go every which way!)

Finally, when the target is in your periscope, fire. If you did everything perfectly and the target does not change speed or course, your torpedo will impact at exactly the part of the ship in the center of your periscope when you fired.


Basically, with respect to rockin robins and crew, what's been named the O'Kane method a way of doing the same thing with the assistance of the tdc.



The limitations of this method are basically:
More workload, the tdc usually takes care of this stuff.
Tactical inflexibility as with the position keeper, you can fire whenever you want to so long as he's in range and you have a good solution. Here, you're limited to firing at a specific bearing.







Even when you have a tdc, there's a hidden advantage to using this method.

It sounds strange if you've never really thought about it before, but with a projectile (whether it's an rock or a torpedo) traveling on a constant speed and course, distance is not part of your firing solution. As weird as it may sound, your lead angle is exactly the same whether shooting at a target 50 feet away or 50 miles away, so long as the projectiles course/speed and target course/speed is unchanging. Diagram it out if you don't believe me .


The obvious advantage of this is that it removes 1 of the 3 questionable elements for your firing solution (range, AOB, speed, ).

The less obvious comes with practice just using dead reckoning. With familiarity, you realize that a target in a certain speed range within a certain AOB has roughly a certain lead angle. For example, a 10 knot target on a perpendicular course has to be lead 13 degrees with a mark 14 on fast. Being able to use dead reckoning on a target that's squirreling around is a nice tool to have in your bag.

[Hitman]

I've been informed that the S-boats did not ever have TDCs fitted to them. Is this information accurate?

Yes. The TDC didn't fit into their conning towers, nor had they space enough in the control room for it.

If S-boats did not have TDCs, was there a means of setting a torpedo gyro angle manually or where they strictly straight run?

They did both. Shooting with zero Gyro Angle is how it was done mainly in WW1, as as such the S-Boats -whose design dates to that era- kept it and worked without TDC. But they had means of calculating Gyro Angles in case the ideal firing position (At right angles to the target course) couldn't be achieved. The Gyro Angles could then be set on the torpedoes while in the torpedo tubes.

They used this for that calculation: http://www.hnsa.org/doc/banjo/index.htm

And this (And also the fleet boats) for computing target data: http://www.hnsa.org/doc/attackfinder/index.htm

You can construct yourself this last tool in cardboard with the templates available in the forum (Look in the sticky for resources), and you can also use a desktop version in your computer done by Gutted, here: http://www.subsim.com/radioroom/showthread.php?t=156698 It has many functions, including the proper attack course for a zero degree Gyro Angle (GA) shot.

I myself do always all my calculations and attacks without TDC when playing with an S-Boat in RFB , and you can bet that I do hit the enemy ships! The enjoyment is proportionally even bigger than simply doing manual targetting (Which is already a good one over the auto TDC)

Good hunting

[Hitman]

It sounds strange if you've never really thought about it before, but with a projectile (whether it's an rock or a torpedo) traveling on a constant speed and course, distance is not part of your firing solution. As weird as it may sound, your lead angle is exactly the same whether shooting at a target 50 feet away or 50 miles away, so long as the projectiles course/speed and target course/speed is unchanging. Diagram it out if you don't believe me .

Not always!!!!


See this thread for further info: http://www.subsim.com/radioroom/showthread.php?t=121744

[ColonelSandersLite]

What I find to be most informative (without even reading the full text even) about the links you provided in your first post is the dates. The mark 8 angle solver is dated 41, so surely the mark 1 was considerably older. At 2 years per major revision, that would place the mark 1 in 1925. More information on when this technology found its way into the boats would be nice if anyone knows.

Originally Posted by Hitman

Not always!!!!


See this thread for further info: http://www.subsim.com/radioroom/showthread.php?t=121744

Actually, yeah always.

Note the above stated caveat that the projectile has to have a constant speed and course *it's very very important*. Firing with a non-zero gyro angle, such as is depicted in that link is no longer a constant speed and course . The torpedo turns at the begining of the run, which obviously alters course, and lese obviously effects acceleration of the torpedo at the outset. You are exactly right in thinking that on a higher gyro angle shot, distance to target becomes more and more important as it takes time for the torpedo to get on course. I'll come up with an in game diagram and post it here.

[ColonelSandersLite]

Here we go, 2 correct firing solutions for the mark 10 torpedo. The only difference between them is distance to impact point. The first is 1000 yards, the second is 3450 yards (just short of the mark 10's 3500 yard range). Note the lead angle is identical


0 Bearing Firing Solution for 1000 Yards:


A Note about the 1,000 yard diagram, I know the tools are not precise enough to get distances to more than 50 yards. What I did was drew a 300 yard circle, a 250 yard circle, and a 3rd circle in between them that was as close to 278 yards as humanly possible.

0 Bearing Firing Solution for 3450 Yards:



I made both of these diagrams at 90 degrees strictly for my convenience. The intercept angle has absolutely no effect on the truth that for a 0 bearing shot, distance does not matter. so long as the target does not alter course/speed.

As a side note, at least with trigger maru, a correct 3450 yard shot with a mark 10 will result in a miss, as the target will certainly avoid it. You don't want to fire the mark 10 at more than 1000 yards because it's just soooooo slow.

On the other hand, more to prove it to myself than anything, I have made 3900 yard shots with the mark 18 (which is slower than the mark 10 but wakeless) using these methods and they work fine if you do everything correctly.


You know, I'm sure I could derive some kind of mathematical formula that would just give me the correct lead angle with target speed, intercept angle, and torpedo speed as variables without the need to draw a few extra things on the map. Frankly though, since you're already plotting the target (you are plotting your target's aren't you?), adding more tools to the process simply makes life harder. Using the method I described above, the only tools I need to figure out a 0 bearing plot are:

Something to get range/bearing to make the plot to begin with. Can be periscope, sonar, radar, binoculars, whatever's appropriate.
Compass
Stopwatch
A pencil and paper
Ruler
Protractor
A Nomograh is nice to have to help determine speed, but not mandatory

As we all know here, all these tools are provided by silent hunter in the map screen where you're plotting the target anyways. Though I swear it might be fun to set up a little coffee table next to my computer and plot things by hand. Might add to the immersion factor .


Oops, made an error (typo) in both those diagrams. Seems I can't type for crap tonight. Fixed.

[Rockin Robbins]

That's a zero gyro angle shot, not a zero bearing shot. In practice, according to the Submarine Torpedo Fire Control Manual, any shot with under a 30º gyro angle was considered "straight fire," with minimal convergence error. So long as the gyro angle computed to that or less, range wasn't much of a concern.

Also, in Hitman's referenced thread, he shows the 90º hook shot there. If you find yourself cleaning up the mess after your initial attack, you sometimes find yourself in the trailing position on a victim you need to finish off. Rather than shooting the zero angle shot from AoB 180, which can be avoided with the smallest rudder correction by the target, the 90º hook shot, impacting at a torpedo track angle close to 90º makes up for a range uncertainty by impacting a hugely greater cross sectional area of the target. It is almost impossible to avoid. That is where you would want to dispense with the zero gyro angle shot for a greater probability of a hit.

You can also imitate the U-Boats and use the TDC as a lead angle calculator for a near zero gyro angle shot (again, any gyro angle between 330º and 30º will do, we have a very large amount of slop to work with, although I try to keep it within plus or minus 10º just because I love unnecessary precision!). Two techniques that use this are the Dick O'Kane and John P Cromwell manual targeting methods.

Finally, the absolute easiest way to set up a zero gyro angle shot with any angle of approach is the vector analysis method. It is easier by far than using any calculator and can be set up in seconds inside the game without alt-tabbing out to a calculator or fabricating one from wood or cardboard.

I maintain the Sub Skippers' Bag of Tricks stickied thread, primarily devoted to these constant bearing firing methods, where range goes out the window and the name of the game is error mitigation. When I get off my lazy butt, gutted's Solution Solver will be added to the links in the first post before his great thread falls off page 1. Actually, the whole quest for adapting U-Boat tactics in fleet boats came from this diagram from gutted, clearly showing that with a zero gyro angle shot range does not matter so long as the torpedo has the range to get there.

[Hitman]

ote the above stated caveat that the projectile has to have a constant speed and course *it's very very important*. Firing with a non-zero gyro angle, such as is depicted in that link is no longer a constant speed and course .

Ahh OK to that but I think it's worth reading my explanation of convergence anyway to prevent users from getting confused

Also, in Hitman's referenced thread, he shows the 90º hook shot there. If you find yourself cleaning up the mess after your initial attack, you sometimes find yourself in the trailing position on a victim you need to finish off. Rather than shooting the zero angle shot from AoB 180, which can be avoided with the smallest rudder correction by the target, the 90º hook shot, impacting at a torpedo track angle close to 90º makes up for a range uncertainty by impacting a hugely greater cross sectional area of the target. It is almost impossible to avoid. That is where you would want to dispense with the zero gyro angle shot for a greater probability of a hit.

I picked that example because it's the one that fits better into a small graphic, and shows more dramatically the problem. The 90º angled shot was used in the U-Boats mainly for the purpose of shooting when positioned between convoy columns. It had the advantage you mention plus the extra distance travelled by the torpedo before turning allowed the trigger pistol to enable after the initial 300 metres run, something otherwise would have been more difficult in such a narrow place as a convoy's interior

[ColonelSandersLite]

You know, now that Robins has showed up and got me thinking about it, I don't think you guys have a tutorial video for no tdc firing solutions. So I just *might* put one together. No promises on that though.

Originally Posted by Rockin Robbins

That's a zero gyro angle shot, not a zero bearing shot.

In an S-boat, 0 gyro is 0 bearing, unless by bearing you're meaning the aiming point which means we've run afoul of a simple semantics problem.

Originally Posted by Rockin Robbins

Also, in Hitman's referenced thread, he shows the 90º hook shot there. If you find yourself cleaning up the mess after your initial attack, you sometimes find yourself in the trailing position on a victim you need to finish off. Rather than shooting the zero angle shot from AoB 180, which can be avoided with the smallest rudder correction by the target, the 90º hook shot, impacting at a torpedo track angle close to 90º makes up for a range uncertainty by impacting a hugely greater cross sectional area of the target. It is almost impossible to avoid. That is where you would want to dispense with the zero gyro angle shot for a greater probability of a hit.

I can see that it's a 90 degree shot . I can honestly say that there is no way in the world I would ever use that to fire at an alerted target. It's true that it nulifies AOB mostly, but Range becomes critical, as well as target speed. Keeping in mind that an evasive target is constantly varying speed and course it's tricky and you can't get an accurate speed. It's true that firing to hit 180 AOB is bad as well, so this is what I would do personally.

Firstly, position myself in a chase position about 500-600 yards back. Set all torpedoes to 0 degree gyro, fast run.

I know that a mark 14/23 firing at a target doing in the vicinity of 10 knots whose course intersects mine at 45 (heading away) degrees requires a lead angle of 11 degrees.

So, what I do is wait for him to start a turn, either to the left or the right, Remember he's evading, so he *will* turn. As soon as I see that, I turn as well and fire a torpedo when the lead angle is each 4° and 7° and 10°. I usually score 2 hits, but actually have scored 3 before. Since he's already turning, he can't dodge in the direction of his turn by turning harder, and simple inertia will pretty much prevent him from turning the other way in time. And if you want to try something really fun, do it with stern tubes while you're in front of him.

In essence, what I'm saying is that when the target is evading is *exactly* when you want to use 0 gyo angle shots, as a full blown firing solution is just too cumbersome. In fact, now that I'm getting fairly experienced in shooting 0 gyro without TDC, I have to say that I've got several rules of thumb memorized that will let me fire at a target and hit him without too much difficulty for most practical speed and intercept angle ranges.


Well, to be honest, if the target is unescorted and alert, I usually just let him open up the distance to around 4000 yards, go to battle stations, order ahead flank, put him 30 degrees off my bow, blow ballast and shoot him with the deck gun. Even in trigger maru the merchant gunners just suck beyond around 2500-3000 yards. If weather permits, I will go to decks awash instead of surfaced totally, that way if I start to take fire that could potentially threaten the boat, I can quickly submerge and wait for the distance to open up more before repeating.

Originally Posted by Rockin Robbins

You can also imitate the U-Boats and use the TDC as a lead angle calculator for a near zero gyro angle shot (again, any gyro angle between 330º and 30º will do, we have a very large amount of slop to work with, although I try to keep it within plus or minus 10º just because I love unnecessary precision!). Two techniques that use this are the Dick O'Kane and John P Cromwell manual targeting methods.

I don't really see how that's specifically imitating u-boats. American subs did not always have TDCs you know . In fact it seems the S-boat, which ironically you used in your cromwell video, should not have one at all.

Besides, you actually can use the tdc without position keeper at any gyro angle you want, even foolishly close to maximum. Try using "O'Kane" on a target coming up your port side and firing at bearing 270. Identical except that you need range. You know where he will be in relation to you so just pick your aiming point, set up the TDC before hand and fire when he's in your sights. Frankly, if you're going to fire at 0 gyro to negate range, I don't see the point in using the TDC at all anymore. Just point the periscope at the correct angle and fire when he's in your cross-hairs.

Originally Posted by Rockin Robbins

Finally, the absolute easiest way to set up a zero gyro angle shot with any angle of approach is the vector analysis method. It is easier by far than using any calculator and can be set up in seconds inside the game without alt-tabbing out to a calculator or fabricating one from wood or cardboard.

Absolutely. Once you've made the leap that when firing at 0 gyro, range does not effect lead angle, it is actually *very* easy to set up a quick firing solution without any calculation whatsoever. Still does have that disadvantage of being tactically inflexible though. The fact that the position keeper will enable you to fire at any bearing regardless of any course changes you make and score a hit as long as the solution is accurate can be a great boon sometimes.

[Rockin Robbins]

Using the TDC to compute lead angle is important because it is very easy to misremember the torpedo speed you are using. After all, we have 46 knot, 31, knot and 10 knot torpedoes. The Mark 14 has two settings, 46 and 31 knots. If you accidentally choose the wrong column on the lookup table, you miss. If you forget to throw the switch into to high speed condition and pick the high speed column you miss.

The TDC knows the torpedo and its speed setting and automatically uses the correct one to set the lead angle. And the TDC allows you to pick any shoot bearing you want, setting the correct gyro angle automatically for your non-zero gyro shots. This versatility approaches that of the German TDC and beats pencil, paper and lookup tables to death!

Successful shooting is all about anticipating errors, eliminating the ones possible and mitigating the rest. In combat one absolute given is that you will make mistakes. The ability to make mistakes and still score is crucial. The only perfect people in war are the perfectly dead.

I always assume that if the WWII guys did it one way they had a good reason. They were just as smart and ingenious as we are. If it were not necessary to use precise terms and language when shooting torpedoes, they would not have done so. But the Submarine Torpedo Fire Control Manual has an entire 11 page chapter devoted to phraseology to implement clear and concise communications among the fire control team. They had no time to waste. If they did it, it was necessary.

Torpedoes don't have bearings, they have gyro settings. Bearings are in relation to submarines. Yes, a zero gyro angle shot in any World War II submarine fires up the submarine's zero bearing. However a 60º gyro angle shot DOES NOT fire up the submarine's 60º bearing. Therefore a separation of terms is absolutely necessary, not a frivolous semantic wordplay.

OH! Destroyers sometimes had aimable torpedo tubes! They were aimed at an angle offset from the ship's zero bearing. So a zero gyro angle shot was never a zero bearing shot there! Just more useless information that you can't use on your submarine, but hey, that's what you get from this neck of the woods.

[ColonelSandersLite]

It's not hard to double check your torpedo speed. It's listed in game in the torpedo loadout screen as you well know. Besides, you forgot the 36 knot mark 10 and the 29 knot mark 18 .

Anyways, you don't need to use any lookup tables. As you said early use vector analysis.

Draw a line representing the target's course.
Draw another line representing your course at the appropriate intercept angle.
Draw 2 circles representing his distance traveled in 3 minutes and the torpedo distance traveled in 3 minutes and place them on the impact point.
Measure the angle with the protractor.
Set your periscope to the angle measured.
Fire when ready.

There's no math and it takes about 45 seconds to do with practice!

Hell, you did it yourself in either your "O'kane" or "Cromwell" video, I just don't know that you realize you did it.

Originally Posted by Rockin Robbins

I always assume that if the WWII guys did it one way they had a good reason. They were just as smart and ingenious as we are. If it were not necessary to use precise terms and language when shooting torpedoes, they would not have done so. But the Submarine Torpedo Fire Control Manual has an entire 11 page chapter devoted to phraseology to implement clear and concise communications among the fire control team. They had no time to waste. If they did it, it was necessary.

Torpedoes don't have bearings, they have gyro settings. Bearings are in relation to submarines. Yes, a zero gyro angle shot in any World War II submarine fires up the submarine's zero bearing. However a 60º gyro angle shot DOES NOT fire up the submarine's 60º bearing. Therefore a separation of terms is absolutely necessary, not a frivolous semantic wordplay.

Yar cap'n, there be semantic reefs ahead!

So, you're saying that that because 0 = 0 and 60 != 60, that bearing and gyro are not interchangeable at the 1 time it's true? Seriously man, just a few sentences before you said something about not being perfect . I'm pretty sure that any submarine weapons officer would understand that a 0 bearing shot means 0 angle from the bow tubes right?

Originally Posted by Rockin Robbins

OH! Destroyers sometimes had aimable torpedo tubes! They were aimed at an angle offset from the ship's zero bearing. So a zero gyro angle shot was never a zero bearing shot there! Just more useless information that you can't use on your submarine, but hey, that's what you get from this neck of the woods.

Of course we're talking about S-boats here, or at the least submarines in general, so doesn't matter really. But speaking of which, I've noticed that some of the Japanese destroyers have these in trigger maru. Will they actually fire them?

[Rockin Robbins]

Originally Posted by ColonelSandersLite

It's not hard to double check your torpedo speed. It's listed in game in the torpedo loadout screen as you well know. Besides, you forgot the 36 knot mark 10 and the 29 knot mark 18 .

Anyways, you don't need to use any lookup tables. As you said early use vector analysis.

Draw a line representing the target's course.
Draw another line representing your course at the appropriate intercept angle.
Draw 2 circles representing his distance traveled in 3 minutes and the torpedo distance traveled in 3 minutes and place them on the impact point.
Measure the angle with the protractor.
Set your periscope to the angle measured.
Fire when ready.

There's no math and it takes about 45 seconds to do with practice!

Hell, you did it yourself in either your "O'kane" or "Cromwell" video, I just don't know that you realize you did it.




Yar cap'n, there be semantic reefs ahead!

So, you're saying that that because 0 = 0 and 60 != 60, that bearing and gyro are not interchangeable at the 1 time it's true? Seriously man, just a few sentences before you said something about not being perfect . I'm pretty sure that any submarine weapons officer would understand that a 0 bearing shot means 0 angle from the bow tubes right?



Of course we're talking about S-boats here, or at the least submarines in general, so doesn't matter really. But speaking of which, I've noticed that some of the Japanese destroyers have these in trigger maru. Will they actually fire them?

Fraid not, at least not yet. There is a crew working on getting AI fired torpedoes into campaign action and that will definitely heat things up a bit when they get it to work properly.

Vector analysis is still subject to the same hazards of getting the torpedo speed wrong, as one of the legs of the triangle is of length proportional to the torpedo speed. Torpedo speed is not always available in the torpedo status screen, depending on the mod you are running. If it is available and you are firing Mark 14s, you can still figure for low speed and shoot high speed or versa visa. It's not a pretty sight. I've done it a couple of times.


Yeah, in a sub, firing out of the stern torpedo tube zero gyro angle is equal to a 180º bearing shot. Of course a sugar boat doesn't have stern tubes, but you can see the precision in terminology is necessary, even in a submarine. It's a nasty requirement because it requires bowing to authority and we're not so good at that in these so-called modern times. But guys mostly dead originated these terms and it's best that we stick to their terms or we start talking gibberish.

Yes, I first taught vector analysis in my John P Cromwell video and it's safe to conclude I knew precisely what I was doing. Nisgeis talked me into teaching it there, and I'm glad I surrendered to his better judgment. I also published a printable 3x5 crib card for vector analysis:



Whether I did so knowingly or not is subject for debate. Naw! Most likely I did it without any comprehension whatever!

[ColonelSandersLite]

Originally Posted by Rockin Robbins

Fraid not, at least not yet. There is a crew working on getting AI fired torpedoes into campaign action and that will definitely heat things up a bit when they get it to work properly.

Glad to hear someone's working on it at least.

Originally Posted by Rockin Robbins

Vector analysis is still subject to the same hazards of getting the torpedo speed wrong, as one of the legs of the triangle is of length proportional to the torpedo speed. Torpedo speed is not always available in the torpedo status screen, depending on the mod you are running. If it is available and you are firing Mark 14s, you can still figure for low speed and shoot high speed or versa visa. It's not a pretty sight. I've done it a couple of times.

I have to admit that I've made a torpedo speed mistake or two, but that got me in the habit of triple checking my torpedo speeds and haven't made that mistake since (knock on wood). In reality, a firing solution goes through a few hands and such a thing would likely be caught, but ah well, it's a game. Besides which, once you get really used to doing without the tdc, you're likely to catch this kind of error by simple familiarity. If you're expecting a firing angle of around 15 degrees and get 24 degrees, you should have that little alarm bell going off in your head.

Originally Posted by Rockin Robbins

Yes, I first taught vector analysis in my John P Cromwell video and it's safe to conclude I knew precisely what I was doing. Nisgeis talked me into teaching it there, and I'm glad I surrendered to his better judgment. I also published a printable 3x5 crib card for vector analysis:

IMAGE CROPPED FOR BANDWIDTH POLITENESS

Whether I did so knowingly or not is subject for debate. Naw! Most likely I did it without any comprehension whatever!

That card is exactly what I'm talking about but there is actually 1 important step that you've neglected in that 3X5 looking at it and should be between 7 and 8. I'm not even sure off the top of my head if I mentioned it even in passing above. If there is *any* chance you have been using the stadimeter since the last game load (like maybe to plot the target or heck, even your previous target) be absolutely sure to send a 0 bearing to the tdc to zero the gyro angle sometime before firing.

If you do not do this, your torpedoes may go off in an unexpected direction. This is another one I learned the hard way. Now, I check it, recheck and triple check it twice! I check it both on the tdc and in the attack map whenever I'm unsure if I've rechecked it recently. You know, this error is *much* uglier than messing up the torpedo speed, so watch out for it!

One last note, if using a bearing plotter with a mod, I don't know about others, but the one that comes in trigger maru is off by 3/4 of a degree (0.75 degrees is really 0 and 180.75 is really 180), so if you're sure the set gyro angle is 0 and the reading on the bearing plotter in the attack map is a *little* off it's most probably fine.

[Hitman]

In case it's useful, I wanted to summarize here the quick procedure employed by U-Boat commanders in WW1 to make zero GA shots:

1.- Up periscope, estimate target AOB, speed (By bow wake and general movement of the ship) and distance (To ensure you are in shooting range)

2.- Put the Uboat at right angles to enemy course. Bearing to target in periscope +90º -Target AOB in degrees = course to right angles.

3.- Look up in the printed table the proper lead angle

4.- Wait for the target to reach the chosen shoot bearing and ... torpedo los!

Actually in the true procedure the U-Boats added/substracted the lead angle to the attack course as defined in the above formula, and sought to shoot with that much deviation from the perfect 90º, obtaining an acute angle that resembles and follows the principles of Rockin Robbins' 45º method. But this 4 steps I described above are the simpliest way to do it all.