Torpedo settings...Real life?

[BigWalleye]

Sniper, please read my last post. I am not, and have never been, talking about the variable which you call "lead angle." I concede that the variable which you call you call "lead angle" is calculated by the TDC. Please either do me the courtesy of addressing my question regarding the aim point offset, or at least stop arguing against claims which I did not make. At the very least, please read my posts comprehensively before replying. Thank you.

[snakedocpl]

Hi Gentlemen,

Originally Posted by Sniper297

I've used both systems, I currently have a German ATO career and a US Pacific career active in SH4, and even though I don't use the PK much I still find the TDC easier to use simply because the "own ship" and "target" dials one above the other makes it easier to visualize the situational awareness "picture" for the approach. I have used the "angle off" method where you estimate the intercept angle, set the fish for a zero gyro angle, then offset the scope 10 to 15 degrees and fire when the target hits the crosshairs, but that's usually reserved for the S-class which wasn't supposed to have a TDC in real life.

If you are sharing with us your experience based only on feeling from SH (and not on a base of real documentation), your opinion is quite irrelevant. Until now, there is no submarine sim with correctly implemented torpedo fire control computer (neither TDC nor TVRe).

Originally Posted by Sniper297

The TDC had the same capability of shooting multiple targets and/or spreading by shifting crosshairs, there was a button on both periscopes and the TBT to send a new bearing to the TDC - if the speed and course of the target(s) didn't change all you needed was a new bearing.

No, TDC had no capability of shooting multiple targets and/or spreading by shifting crosshairs (if we are talking about real TDC Mark 3). The reason: there was no connection between target bearing transmitters (at periscopes or TBT) and TDC (or more strictly with Position Keeper).

Source document: https://maritime.org/doc/fleetsub/elect/chap14.htm#14C

At TDC were only target bearing receivers, which were observed by TDC operator and their value was compared with the target bearing value generated by Position Keeper. If these values matched, the target data (course, range and speed) entered to the Position Keeper were correct, if not - the target data has to be adjusted.

Here you have the functional diagrams of Position Keeper and Angle Solver and there are not electrical inputs for target bearings.
https://maritime.org/doc/tdc/pg068a.htm
https://maritime.org/doc/tdc/pg086a.htm

BTW, the only values electrically inputted to TDC were own speed and own course.

So you could train the scope and TBT and it does not influence the solution at all.

Similarly, the TDC did not calculated the spread angle. The spread angle had to be calculated by human and entered manually to the Angle Solver as so called Offset Angle. The Offset Angle modified the gyro angle entered to the torpedoes, so the Offset Angle handle had to be trained after launching each torpedo in salvo.

Originally Posted by Sniper297

And the TDC had enough sense to fire at where the target would be rather than where it is at the moment the button was clicked, that's lead angle. I agree that the actual lead angle is nice to know if for no other reason than a double check on the accuracy of the TDC solution, but I'm sure there was someone on the plotting team responsible for checking that. Many skippers had someone on the attack team standing by with a "banjo" and Is/Was just in case, especially early in the war when the TDC reliability was still unknown.

As I explained above, there was no button. TDC philosophy was to have ability to fire without periscope. I mean, if you entered the correct values to the Position Keeper, it continually calculated the correct relative position of the sub and target. Based on the output from Position Keeper, Angle Solver calculated continually the correct gyro angle, so you can shoot any time, without seeing the target.
The periscope target observation were done to check the accuracy of the Position Keeper solution. The TBT/Periscope operator shout "Bearing Mark!" or pushed the button, and the TDC operator compared observed target bearing with target bearing generated by Position Keeper. If target was at position calculated by Position Keeper, everything was ok, if not, target data has to be adjusted. It was iterative process.

Originally Posted by Sniper297

I don't know how you figure the TDC didn't have lead angle capability, target speed, relative bearing, and AOB equals lead angle - which was automatically updated in the torpedo gyrocompass. Put the crosshairs on the target, hit the button to send the latest bearing to the TDC, which sets the gyro angle for the correct lead angle, and shoot. Don't even need to know the lead angle, TDC sets that automatically.

Most of misleading information were corrected above. One more: torpedoes were not fitted with gyrocompass (which is devices based on fast-spinning disc and the rotation of the Earth, using the effect of gyroscopic precession, used for finding true north), but with gyroscope (device based on fast-spinning disc, used for determining fixed direction in space).

--
Regards
Maciek

[CaptBones]

Although this thread is way off track from the questions in the original post, there is a lot of good information in it, as well as some not particularly good, or useful, information also. The discussion has not only been “spirited”, but respectful as well, which is something that isn’t typical of most forums on the internet; that is a feature of the Subsim community and its members that I really find to be refreshing and somewhat “comforting” as well. Nice to deal with people who can be civilized and respectful, despite their different opinions and points of view. A large part of this discussion is simply semantics, which everyone seems to be dealing with without a lot of fuss. But, on to a couple of my own comments; regarding the USN TDC only.

snakedocpl has identified a couple of things that are quite correct in the differences between the real world TDC and the “object” we use in the game. I would add my own semantic problem first, that there is no such thing as a ”lead angle” used in USN submarine torpedo fire control solutions. In the real world, target speed, relative bearing and AOB do not equal a “lead angle”. The geometry of the solution is more complex and consists of own course, target course, target relative bearing, angle on the bow, range to target, distance to target track, gyro angle and track angle…which doesn’t produce a simple “lead angle.”

Why? Well, as was mentioned, a “lead angle” is what a shooter uses when firing at a moving target. The statement was then made that unless you’re shooting at a moving target you don’t need a lead angle. That may be true if you’re a hunter or marksmanship shooter or on a fixed gun battery. But in submarine warfare, whether the target is moving or not, the shooter is moving and generally so is the target; plus, they are usually both moving on different paths at different speeds. Determining the correct “lead angle” is a much more complex problem. Then on top of it all, we have the torpedo itself and its gyroscope.

The torpedo cannot instantly turn to the proper intercept course when it is fired. First of all, dealing with WWII torpedoes, the gyro isn’t powered up until the fish is fired and it takes a few seconds before it is stabilized and functioning. The torpedo thus runs blindly straight ahead (we hope) before taking the gyro angle input set by the fire control system and turning onto the intercept course. Then, you have to recognize that the fish can’t turn on a dime either…its course change involves the same kind of advance and transfer geometry that the firing sub and its target both also have. It would be nice if the angle between the line of sight and the torpedo track was a simple angle, with the opposite side equal to the target run during the time the torpedo takes to reach the target track.

But it ain’t so. The geometry of the torpedo track seriously screws up the simple solution. The good thing is that the real world TDC ”knows” what the geometry of the torpedo’s turn to the intercept course will be…or should be. In the game that turn is instantaneous and our TDC does calculate an actual “lead angle”. Back in the real world, you’ve also got to deal with things like changes in the target’s course and/or speed as well as necessary changes in the sub’s course and/or speed. That’s where the manual plot takes over and compares the DRT trace of the actual tracks of the sub and the target with the TDC solution. The plotting team was the key to accurate firing, especially at a zig-zagging target, single ship or convoy.

One final note…snakedocpl mentioned a key factor regarding the TDC; provide fire control solutions without visual observations. It was developed prior to the war, when USN doctrine was for firing at 100’ depth on hydrophone bearings only. The resulting “automatic fire control procedure” was almost completely useless. The submarine COs didn’t simply prefer something else, they had to come up with better methods in order to have any chance of success at all. Dick O’Kane himself once commented that he (along with Dudley Morton and many others) thought that about the only real useful features of the original TDC were the Position Keeper and that it accounted for the geometry of the torpedo’s turn to the intercept course and then calculated the gyro angle correctly.