Historically-Accurate TDC Usage

[KlassenT]

I've been playing around of late with all manner of attack families in SH4, and at the end of the day, I have to say that I just don't come away with any feeling of trust in the TDC's "selling points." It's great for data acquisition / input and crunching some numbers for gyro angles on less conventional shots, but when the rubber meets the road I'm infinitely more confident using some sort of geometric approach.

The question, though, how does that stack up with the actual skippers in the earlier days of sub warfare, before we had the serious computing power to handle complex fire-control problems? Certainly the math behind vector analysis and the concept of 3min diagrams are older than even the rustiest of S-boats, so how many skippers ended up putting their trust in their TDC instead of their pencil and notebook? I've never had the privilege of reading most of the WWII-oriented books that come to such high acclaim here on the forums, and I'm certain there are several capabilities of the TDC that never got properly modeled into SH4's gameplay, so what's the skinny on this one, fellas?

[SH4 fan]

I would like to know that as well.

I usually set up a geometric approach with the TDC preset with some known easy round distance and the AOB, as the ship passes the preselected point I punch the PK and update as necessary.

[Bilge_Rat]

yes, the TDC was in use in all the U.S. Fleet Boats (but not the S-Boats) from dec. 41. The newer boats all had the Mark III. It worked pretty much as in the game and skippers were using it from the start of the war to compute a firing solution.

look here for more "official" info:

http://hnsa.org/doc/tdc/index.htm

I had checked that myself when the game came out since the in game TDC seemed far too advanced for a WW2 submarine, but this was one area where the U.S. was technologically ahead of other navies. Even the in game stadimeter appears to work as the real ones did, although many skippers calculated the range manually and they of course, did not have access to info as accurate as what we have in the recognition manual.

if you look here in chapter 7, you see the three main types of attack methods used by U.S. boats:

http://hnsa.org/doc/attack/index.htm

[Wilcke]

It really depended on the Skipper, XO and firing party, in my readings regarding TDC users some of them became very adept and deadly in its usage. Others not so much. The current TDC in SH4 is lacking in some of the functionality. Still it has its value in certain situations, but again one can get lazy and just do the Dick O' Cain thing and be done with it!

[Keelbuster]

I would like to know that as well.

I usually set up a geometric approach with the TDC preset with some known easy round distance and the AOB, as the ship passes the preselected point I punch the PK and update as necessary.

That's exactly what i do. I still like the german TDC better; seems more natural, and I found it easier to make relatively accurate 'snap' shots. Plus, the german salvo control is great.

[Keelbuster]

yes, the TDC was in use in all the U.S. Fleet Boats (but not the S-Boats) from dec. 41. The newer boats all had the Mark III. It worked pretty much as in the game and skippers were using it from the start of the war to compute a firing solution.

look here for more "official" info:

http://hnsa.org/doc/tdc/index.htm


http://hnsa.org/doc/attack/index.htm

Very cool reading! If only we had this level of detail simulated in SH4 (e.g., all the commands given to the operators, the speed rulers, and all the additional features...)

[Nisgeis]

This is going to be qute random, so apologies for that:

The in game TDC doesn't really match up to a real TDC. In many ways it's a poor version of it, with lots of functionality crippled or missing. The chief crippled feature is the adjustment of the bearing, which messes up the target course, which destroys your whole solution and causes lots of frustration for new users of the TDC.

The real TDC had a number of key features, the chief one was the PK, which allowed the submarine to manouver and have all the relevant target position still be updated correctly, if you changed course or speed.

Another main part it had was the SBC, the sound bearing converter. This device takes the target speed and course into account and allows sound only bearings to be converted into actual bearings. As sound takes some time to travel through water, this can cause the sound to be on a different bearing to the actual bearing of the propellers, as the bearing will lag behind. This is made worse by the propellers being at the back. The SBC took the target length and speed and course and worked out for you, based on the sound baring, what actual bearing the MOT was. This is of no use in SH4, as in SH4, sound travels instantaneously, so sound bearing are the same as optical bearing.

The mark 3 TDC operated within a target range of 400 - 8,000 yards, with the mark 4 operating between 400 and 40,000 yards. The mark 4 TDC also had an extra receiver section, which had repeaters for all the sensors, e.g. radar bearing, sonar bearing, optical bearing and range repeater from radar, stadimeter and sonar. This reduced the amount of communication necessary and therefore also reduced errors. Note that this wasn't an automatic entry, it was just a repeater display.

One feature that isn't implemented is the ability to control time in the TDC. You can wind time forward and backwards. To take an example, let's say you were trying to intercept a fast convoy and you knew you couldn't get ahead, as they were travelling faster than you, so what you could do is wind the time forward and watch the range and see at what point you would be closest to the target. E.G. in 3 hours 27 minutes we will be the closest to the target. You can also wind time back to the start and put in a different speed and then wind forward to your second onbservation and see how the two compare. Or put in a different course or whatever.

The main use though is the PK being upto date on the historical data, so that you can compare bearings and ranges with the observed ranges. Doing that you can detect zigs toward or away or changes in speed more easily than doing it on paper.

O'Kane used the TDC by having the operator wind the bearing backwards, thus holding the bearing at the same bearing as the periscope or UZO, which effectively allowed him to accurately aim at the point at which his line of sight intersected the target's course and maintain an accurate torpedo gyro angle for that point, which is something that you can't easily do with verctor analysis on the fly, unless you are on a pre-calculated and fixed course.

Er, other things the one of the versions of the Mark 3 had was a range to track indictaor, which would tell you how far you were from the target's track, which is useful if you want to avoid being too close or too far away from the target when you get in position.

[Bilge_Rat]

I usually set up a geometric approach with the TDC preset with some known easy round distance and the AOB, as the ship passes the preselected point I punch the PK and update as necessary.

How does that work?

I basically follow the method set out in the manual, with my own refinements:

1. ID ship (enter in TDC);
2. get first range reading from stadimeter (enter in TDC);
3. start stopwatch;
4. plug in observed AOB (enter in TDC);
5. plug in trial speed (from sonar station, i.e. "slow", "medium") (enter in TDC);
6. start PK;
7. plot estimated TGT position on NAV map (based on range and bearing in #2 above) (i.e. Mark #1);
8. after 3 minutes as shown on stopwatch, determine new range with stadimeter (re-enter in TDC);
9. plot new estimated TGT position on NAV map (based on range and bearing in #8 above)(i.e Mark #2);
10. draw line from Mark #1 to Mark #2. From this you can reasonably estimate TGT's course and speed;
11. plug in new observed AOB, as determined from course in #10 (re-enter in TDC);
12. plug in calculated speed from #10 (re-enter in TDC);
13. fire torpedoes, based on best range as shown on the Attack Map.

It is a bit cumbersome, but highly accurate. Obviously, I may have to refine the solution between 12 and 13, based on observation of the TGT and how it matches up with the TDC solution.

[Bilge_Rat]

The chief crippled feature is the adjustment of the bearing, which messes up the target course, which destroys your whole solution and causes lots of frustration for new users of the TDC.



could you explain that Nisgeis, I am not sure what you are referring to.

[SH4 fan]

How does that work?

I basically follow the method set out in the manual, with my own refinements:

1. ID ship (enter in TDC);
2. get first range reading from stadimeter (enter in TDC);
3. start stopwatch;
4. plug in observed AOB (enter in TDC);
5. plug in trial speed (from sonar station, i.e. "slow", "medium") (enter in TDC);
6. start PK;
7. plot estimated TGT position on NAV map (based on range and bearing in #2 above) (i.e. Mark #1);
8. after 3 minutes as shown on stopwatch, determine new range with stadimeter (re-enter in TDC);
9. plot new estimated TGT position on NAV map (based on range and bearing in #8 above)(i.e Mark #2);
10. draw line from Mark #1 to Mark #2. From this you can reasonably estimate TGT's course and speed;
11. plug in new observed AOB, as determined from course in #10 (re-enter in TDC);
12. plug in calculated speed from #10 (re-enter in TDC);
13. fire torpedoes, based on best range as shown on the Attack Map.

It is a bit cumbersome, but highly accurate. Obviously, I may have to refine the solution between 12 and 13, based on observation of the TGT and how it matches up with the TDC solution.

I don't even need to ID the target. I don't always use, 11,000y and often times will use less if time permits but it is an easy input since it is the max range on the stadimeter.

1) track radar target
2) calc time, speed, distance, and course.
3) plot 90° to target course.
4) measure distance to target course
5) Plot 11,000y (5.4nm) from me on enemy course line
6) measure AOB from that point
7) input speed, AOB, distance in TDC
8) watch target pass 11,000y mark
9) activate PK
10) adjust speed and range as necessary
11) let the fish swim.

All triangles add up to 180 so even if it is not a 90° intercepts all you need to do is, AOB = 180 - (course intercept angle + RB to target)

It is a very accurate method, I only use the periscope to refine the final solutions and ID the target.

[Bilge_Rat]

I don't even need to ID the target. I don't always use, 11,000y and often times will use less if time permits but it is an easy input since it is the max range on the stadimeter.

1) track radar target
2) calc time, speed, distance, and course.
3) plot 90° to target course.
4) measure distance to target course
5) Plot 11,000y (5.4nm) from me on enemy course line
6) measure AOB from that point
7) input speed, AOB, distance in TDC
8) watch target pass 11,000y mark
9) activate PK
10) adjust speed and range as necessary
11) let the fish swim.

All triangles add up to 180 so even if it is not a 90° intercepts all you need to do is, AOB = 180 - (course intercept angle + RB to target)

It is a very accurate method, I only use the periscope to refine the final solutions and ID the target.

I see what you are doing, I can follow from 3 to 11.

But how do you calculate 2 from the Radar? Do you plot it on the map?

[SH4 fan]

Yup. I cheat a little bit and pause to get a good mark on the map. Then at x seconds plot point 2. That gives speed and course. then i extend the plot and revise as time goes. Since I am a bit of a perfectionist I use my TI-83 for the speed check. I wrote a program to take the yards traveled and time (s) and find speed in knots.

Basically it just does (10800/6076)*(dist yards/seconds) which comes out to knots.

I also have an AOB program which does the following. I dont use it very often because I just set up a triangle and measure the angles by hand. But it comes in handy.
Ship: Length = L
Ship: Mast height = H
Ship: Ratio = L/H = R (R for ratio so i remember what it is)
Observed Aspect ratio (tick marks, this one you put in as a division ie (7.5/4.3)) = O (O for Observed)
Actual vs Observed Ratios = O/R = R (this replaces R in the memory with the new ratio)
arcsin(R) = A (A for Angle)
------------------------
Optional (i keep my calculator in radians)
A*(180/pi) = A
A now is the AOB in degrees!

[Nisgeis]

could you explain that Nisgeis, I am not sure what you are referring to.

OK, you know how the German TDC is linked to the periscope, so that once you have the target course layed in, if you move the 'scope then the AoB gets updated, so the solution is correct?

Well, the US TDC has a similar feature. Let's say you are tracking a target at a speed of 6 knots, on a course at 90 degrees to your own course. If you suddenly notice that the target is gong much faster than you thought and you update the bearing, then in the real TDC, the range and AoB and everything do do with it would be updated at the same time, as the PK moves the ship along its course with a bearing change. Note that the TDC is not directly linked to the periscope, because that would mess up the PK, which is the fundamental reason why it is not directly connected, but the functionality of the German TDC is there.

In the SH4 one, you have to guess or measure with the stadimeter the range again at the same time as you send the bearing (as you have to send both together D'OH!), as otherwise it will still use whatever range it had as it isn't connected, but worse than that, it will still use the AoB it already without updating it based on the bearing change, so if you advanced the bearing by 10 degrees, the AoB used would be the old one prior to your change and therefore the target's course would be changed by 10 degrees, which would make a mess of your solution.

So, what would be a simple bearing change, means you have to re-enter everything again, hardly the refinement of a solution the TDC was designed for. It also ramps up the amount of work you have to do if you discover an error at a late stage of the attack.

[KlassenT]

Well, I suppose it all goes to show you there's more than one way to skin a Maru (Though do pardon the sheer irony if you're a fan of everyone's favorite box-sliding Scottish Fold.) What I meant when I initially mentioned geometric approaches was much more related to on-the-fly solutions like vector analysis rather than the methodical approaches wrought with terrible, initimidating things like theories and axioms. :D

I suppose I ultimately view the TDC moreso as a tool to gather data, rather than the means by which a final firing solution is calculated. It can certainly do some very impressive things for its time. The PK is the thing that really stands out most to me-- its capability to combine several inputs from devices like the periscope and stadimeter (which I can only presume were all analog) and manage them in unison with movement compensation really is nothing short of extraordinary for period technology. But even with that said, when it comes time to take an approach track and compute a firing solution, I find most of those impressive features to be extraneous when I can put pen to paper and come with an equally effective firing solution as I could fumbling around with all the dials, bells, and whistles while still grappling with ensuring device accuracy for all the data I've manually fed into the equation (Speed, etc.)

Maybe I'm just the nerdy sort that has faith in the fact numbers don't lie, and it's significantly easier to verify a calculation than it is to cycle through all of your data at-hand, make sure it's timely and up to date, then double-check that it's all been entered correctly. Perhaps I've thus far just been siding with vanity in assuming that cranking out a good null-gyro shot was equally simple for most folks as feeding everything into the TDC, but my curiosity is still piqued about how WWII skippers viewed it... I suppose I'll just have to bite the bullet and go pick up the chronicles of the Wahoo to start my library! :yeah:

[sckallst]

It's too bad that the in-game TDC is not as functional as the "real" one. That said, the PK is very nice. The weird thing though is that as you get better and better at planning attacks (at least from the moment of visual contact on in), some of that functionality becomes less important as you minimize the amount of extraneous movement on the appraoch that makes the PK most valuable.

This is getting off on a tangent just a bit, but I thought I'd mention it in relation to plotting. I play exclusively with no map contacts. For the longest time I got hung up on trying to plot things on the nav map dynamically (in other words, on the fly). For those that do this, and try to be accurate, it's stressful and really hard to do for one guy. The worst part is always having to hit your marks "on time".

I've also used the MoBo application which is way cool. But, in learning how to do that and just digging into this subject matter in general, I've swithced away from navigational plotting to actually doing manuevering board/relative motion solutions "off to the side" on the in-game nav map. The tools are there to do it (using the compass as an improvised parallel ruler). The greatest advantage to plotting this way, over trying to do a dynamic nav plot, is that you mostly free yourself from the need to be "on time" all the time. It's made me into a better player, given me greater insights into the whole subject matter of the game, and it's just rewarding in an of itself. Of course YMMV, but for someone looking to expand their library of knowledge/techniques I recommend it. I may even get around to doing a video of how to do this some day. In the meantime, I'll look up the links for a couple of pdfs from which I learned the basic stuff and post them if anyone is interested.