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CaptBones · 04-27-17, 02:30 PM

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.

04-27-17, 02:30 PM	#18
CaptBones The Old Man Join Date: Nov 2010 Location: Rockton, IL Posts: 281 Downloads: 208 Uploads: 0	otato...potahto 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.