[Nisgeis]

I did initially start this as a small paragraph on what was wrong, but well, look what happened! I too had problems when I first tried manual targetting and I though it was important to not only explain how to do it properly, but to explain exactly why it wasn't working, as that's the real key to understanding the proper use of the TDC.

Hi jgbishop. I followed your instructions to the letter and I also missed about half a ship length to stern. Your TDC is just a computer that can very quickly compute all aspects of the target and yourself, but it's got no common sense. It's basically a really fast idiot.

What it belives is going on, is determined by the data you tell it and the order you tell it in. The TDC will compute target course based on all information it has, however wrong that information is. To try to explain what's going on, the following explains what you think is happening and what the TDC thinks is happening. Just remember, Captains are from Mars, TDCs are from Venus.

Anything in green is correct information that the TDC has and red is incorrect at the time of the operation given.

1. Identify the ship (Mogami Heavy Cruiser).
TDC Knows> ALL DEFAULT - Range: 547, AOB: 0, Bearing: 0, Speed: 0
TDC Thinks> Target is dead ahead with bow pointing directly at the submarine, 547 yards away and stationary.

2. Find the range to the ship with the stadimeter (this I can do). Send said range to the TDC.
TDC Knows> Range: 1600, AOB: 0, Bearing: 321, Speed: 0
TDC Thinks> Target is on bearing 321, 1600 yards away and stationary.

3. Ready a few torpedoes.
TDC Knows>Range: 1600, AOB: 0,Bearing: 321,Speed: 0
TDC Thinks> No Change. (Target data is decaying. range and bearing have become incorrect - bearing rapidly decays.)

4. After some time, take another range to the ship. Again, send to TDC.
TDC Knows> Range: 1500, AOB: 0, Bearing: 326, Speed: 0
TDC Thinks> Target is on bearing 326, 1500 yards away and stationary.

5. Start position keeper.
TDC Knows> Range: 1500, AOB: 0, Bearing: 326,Speed: 0
TDC Thinks> I'm now tracking a target that is on bearing 326, 1500 yards away and stationary. Target heading is 146 (derived from AOB, target bearing and submarine's own heading. Note that this heading is incorrect, as it is derived from data that is not correct as the AOB is wrong.)

6. Estimate speed and bearing (I'm using the estimate button on the speed dial).
NOTE: The only way to send new bearing information with the periscope is to use the 'send range and bearing to TDC' button. You're not clear whether you are just sending the speed information (which does not send new bearing data) or whether you are sending the speed and then sending the bearing by sending the range again (which will give the wrong range, unless you retake it with the stadimeter). I'll assume for the sake of this explanation, that you have just sent speed.

TDC Knows> Range: 1500, AOB: 0, Bearing: 326, Speed: 9
TDC Thinks> I'm tracking a target that is on bearing 326, 1500 yards away and is steaming directly towards me at 9 knots on a southeasterly course of 146. NOTE: This makes the TDC rapidly decrease the range between you and the target at a rate of 100 yards every 20 seconds, as it thinks it is steaming towards you, instead of accross your bow. This error is compounded by the bearing also being incorrect, when the proper bearing of the target is changing, as it is steaming accross your bow. All target data decays, but this is now a solution for a problem that does not match reality, so all target data (except speed) is being actively corrupted. What is actually happening is the range is changing fairly steadily (it should reduce a bit and then increase as the Mogami crosses your bow) and the bearing should be changing quite fast. The TDC however has the bearing as static and the range changng quite fast.

If you had sent range and bearing to get a new bearing to the TDC, the bearing and speed would be correct, but the AOB and Range would be incorrect and the TDC would still think the target was steaming directly towards you at 9 knots, on the correct bearing but but further away that it actually was. The calculated course would also be incorrect. This would also cause the data to rapidly become corrupted (except of course speed). The bearing would also still be static and the range rapidly changing, which as we know should be the other way round.

7. Adjust angle on bow to match computed heading. Send to TDC.
TDC Knows> (Depending on how long you take to do it) Range: 1100, AOB: 70, Bearing: 326, Speed: 9.
TDC Thinks> Now tracking a target steaming NE accross submarine's bows, range is 1100 and steaming at 9 knots. This solution is wrong, the TDC believes the ship to be on the wrong bearing, so it will interpret the AOB you give it as incorrect and derive a course that is 076 (instead of 090 as it should be). This point may be a bit confusing, so let me explain further:

In the Torpedo Training exercise, the Mogami is steaming on a course that is roughly 090, or due East. You are pointed 000 due North. Imagine you take a range and bearing when the Mogami cruiser is at bearing 326. With the AOB incorrecty set at 0 degrees, TDC calculates that the Mogami's course is 146 (approximately SE). Then, things get even worse.

To illustrate the point I will exaggerate things and let's say we wait between range and bearing taken at bearing 326 and taking the AOB measurement. The cruiser will steam across your bow and will end up dead ahead at a bearing of 0 degrees, so let's say that you use this opportunity to get a really accurate measurement of the AOB and as it dead ahead and at a right angle to you, the AOB is 90 degrees to starboard. If you send this AOB to the TDC, the TDC will calulate the Mogami's new course based on the bearing it previously had and will track the target from this point. Unfortunately, as the TDC still thinks the Mogami is on bearing 326 and not bearing 000 as it actually is, it will think you are now telling it that the Mogami has suddenly turned from steaming directly towards you, through 90 degrees to port and that you are now abead of the Mogami. The TDC calulates the new course, based on bearing, AOB and submarine's heding. A 90 degree turn to port on a ship travelling SE would now mean that the ship is travelling NE on a course of 056 and this is the value that the TDC gets from the wrong bearing, correct AOB and correct submarine's heading. The course is incorrect by 34 degrees (056 compared to 090) and this matches the difference between the correct bearing to target and the incorrect bearing the TDC has (326 compared to 000).

The rate of error between actual course and TDC generated course depends on how long you wait between sending range and bearing and the AOB to the TDC. The timing of this is particularly important on targets that are at extremely close range, as both their bearing and AOB change rapidly the closer to you they are.

As you can see, your current soluton now has the target too close, on the wrong bearing and on the wrong course, but the speed is good. The solution, as inaccurate as it is will get rapidly worse the longer you wait to fire and any topredoes fired will be aimed by the TDC aft of the ship.

8. Fire torpedoes.
TDC Thinks> This one's in the bag!
Result: Miss. Miss. Miss. Captain... Report to the SS Garbage Scow.

It doesn't really matter when you start the Position Keeper, the key is to send it data regularly and to be aware of what affects what. You should try to make sure that ALL data is as up to date as possible. It is best to estimate the AOB and speed first, send them to the TDC and then send the range and bearing. The reason for this is that the bearing is the MOST accurate reading you can obtain, so sending this last will reduce the amount of error creeping into the solution, by resetting the aiming point. Errors in the AOB, range and speed will introduce errors over time, at a rate depending on how inaccurate your estimates are. As long as you are attacking your target from a position from which the target's length is optimal, or near optimal (as long a target as possible) then 10 degree errors in the AOB and a few hundred yards error in range don't matter that much as long as you use a reasonable spread.

Experiment with different spreads. I try to use an 80% spread, which means that if I aim at the centre of the hull with 4 torpedoes, then all four should hit, with tropedo no. 1 hitting near the stern, no. 2 hitting aft of the centre of the hull, no. 3 hitting forward of the centre of the hull and no. 4 hitting near the bow. A 150% spread would mean that if all torpedoes were aimed correctly, the torpedoes would spread out to a distance of 150% of the length of the ship aimed at, so not all would hit, but you would have more chance of hitting, albeit with less torpedoes. This is good for when your target data is poor or hard to obtain (can't see waterline due to rough weather, for example).

The key to using the TDC is to give it the best data you can, with as short an interval between the speed, AOB and range estimates as possible and to check it and re-enter is necessary. You can put in your first reading and then a short while later, check the generated target data from the TDC generated when the Position Keeper is switched on and compare it to the data you can observe. The TDC will calculate where the target will be, based on the information it has been gven. If you have given it 100% correct data, the generated bearing, range and AOB will all match what you can observe. If the generated data doesn't match, then the solution is not correct. It's important to note that if your solution isn't correct, then simply resending a new range and bearing won't correct it. Assuming you have identified the target correctly and the range is fairly reliable, then you either have the target speed or the AOB wrong.

Incorrect speed will mean that the target's generated bearing advances too fast if you have estimated the speed to high, or doesn't advance as fast as observed if you have estimated the speed to low. In the torpedo training exercise, if you estimated the Mogami at bearing 326, range 1500, speed 12 knots and ran PK for a while, the TDC would generate a solution for where it should be if the data is correct. If the generated bearing after 1 minute says it should be 346, but it is actually observed at bearing 336 then it's likely you have the speed estimated wrongly. Reset the target speed to 6 knots (as the bearing was 20 degrees advanced instead of 10 degrees), send to TDC then resend AOB and Range and bearing. Run PK for another minute and match the generated bearing to the observed bearing.

If the bearings match and you have identified the target correctly, then you probably have the correct speed. It's possible of course that you got the AOB wrong and the target is steaming towards you or away from you at a steeper angle. If this is the case, then you will find that the generated range does not match the observed range. If you find the range is consistenly observed as being closer than the generated solution says, then the target is closing on you faster than you thoguht and the AOB is too high and needs to be reduced (ship turned so that the bow points more towards you), to give you a course that is closing faster. If the range is increasing, the AOB is too small and needs to be increased (bow turned to point further away) as the target is steaming away from you.

If the target is steaming away or toward you on a different course, once you have the correct course, you will need to increase the target's speed and send it to the TDC, or the generated bearing will lag behind the observed bearing.

Small errors on the AOB and speed don't matter that much, just experiment and see what happens.

Make your TDC do the work and make it tell you what data is correct. Compare generated data to observed data and you'll soon get the hang of what the TDC is all about. I've made shots on tankers at 8,000 yards using the TDC to correct itself like this and that's very satisfying.

You should also look into the O'Kane method, as that may suit you better.

Sorry this is so long, but I hope it helps.

Nisgeis.