how to re-set the tdc

[Rockin Robbins]

Originally Posted by Joe S

I assume you got the Dick o'Kane method from one of his books, both of which I have read , but not recently. If you did get the method from his books, can you tell me which one and approx where so I can re-read that section?

You probably already know this but maybe some people do not: once you establish the amount of lead in degrees for a given target speed, that angle of lead is good no matter what the range. In the example you gave in the above referenced post, a lead of 9 deg was used based on the speed of the target. If you have an accurate target speed calculation, all you have to do is aim the torpedoes the given amount of degrees ahead of your desired point of impact and you should get hits.
I believe your method is sound, but have not tried it. After I try it I may have a few more questions. Thanks for your help. Joe S

In his books, O'Kane tells how he dispenses with the necessity of knowing the precise range and turns off the position keeper during some attacks. With the help of aaronblood and gutted, we reasoned out that the most likely type of attack which met those characteristics was a modified Fast-90 attack from the U-Boats. Gutted had made a chart showing the lead angles for German torpedoes, which he modified for fast and slow Mark 14's.

For the fast-90 attack to work, you look up the lead angle for the target speed. First you set the torpedo to run up the zero bearing. Then you point the periscope at that angle before 0º, 360 minus the angle for targets moving left to right and the angle for targets moving right to left. As juicy parts of the ship cross the crosshairs, shoot.

Then it was left to me to figure out how to use the blasted thing. At the time we were all under the impression (the manual said so) that in order to work the stadimeter the periscope had to be locked on a target. This was bad. So I loaded up WernerSobe's Natural Sinking Mechanics test mission and went to work. After much trial and terror, I found that the periscope didn't have to be locked on anything to send a bearing. You didn't even have to use the stadimeter when you sent a bearing. You could set the torp track across empty water by pointing the periscope at a bearing and pressing the send range/bearing button. Then you sent a bearing without a range. Perfect!

So I set up for a fast-90 with gutted's chart. 9 knots = 11º, blah, blah, blah, shoot! And the torpedo passed well in front of the target. @#$@#$%@#$$!!!! I analyzed the attack and found that I had used the column for slow torpedoes on a fast torpedo. And I realized that you would have to have a separate column for Mark 18s and cuties and... This is so complicated nobody will be able to hit anything. What now?

There was only one option: find a way to toss gutted's chart. And then I realized that we already had a chart that picked its own column: the TDC! As long as the PK was off, all the TDC did was calculate the lead angle for a target moving at a certain speed for a selected torpedo. So the Dick O'Kane technique was born. No more chart!

Now, you measure the speed of the target and enter it into the TDC. Doesn't matter which direction it's moving in, you set that with the AoB. Now you set the AoB for 90º minus the number of degrees from zero you're going to shoot! If you're going to shoot at 350, your AoB will be 90 - 10 = 80º. Your target is moving left to right so your AoB will be starboard (right) 80º. Lastly we'll select a forward torpedo tube, point the periscope at 350º and press the send range/bearing button. OK, now maybe 15 minutes before you shoot we're all set up and all we have to do is wait. You can look all around with the scope and not mess up the shot.

OK, here comes the boat. You don't even have to keep the scope up, just look at the sonar bearing and take a peek now and then to make sure he hasn't changed course. You're a hole in the water here. When the sonar bearing gets to about 340, raise the scope and point it at 350. Open up a couple of tubes. As the front crane passes the crosshairs, shoot. Cycle to the second tube and shoot it as the aft crane is in the crosshairs. Two booms will follow and the ship goes down. You had the whole shot set up 15 minutes before the ship got there!

Is that as easy as it gets? I think so.

[Joe S]

I was just about to post another message when I saw your recent post. In the course of trying this out, I discovered, I think, that you need to set the range to something in order for it to work, so I set it at 1500. First, of course, you set the target speed. Then set aob 90 left or right depending on the setup. Then set range to 1500. THEN, pick a target. Aim the scope where you want to hit, click the send bearing button and shoot. Move the scope a few degrees to the next spot on the target and shoot agian. Pick another target. Aim at a spot on the target, click the range button and shoot. Pick another spot on the target and shoot again. (too bad the game doesnt automatically select the next tube) so far, in my limited testing, you need to click the send range button for each target but not each shot. I havent tried it in an ideal setup, with two or three targets between 350 and 20 degrees and under 2500 yds but so far in the Borneo mission I have been getting hits on multiple targets, not 100%, but definately worth pursuing. Thanks! JOe S

[jazman]

It's funny, but I'm pretty bad at everything except for the O'Kane method. Somehow that method has "taken", I even figured out all the trigonometry.

I've tried with the PK all sorts of ways, and I just can't get range right. I hate the Stadimeter and all its works.

[Joe S]

Jazman,

forget about the range, it means nothing. The reason is, once you know the amount of lead, the angle of lead stays the same no matter what the range. I normally set the range with the rangefinder, but I use averages for the type of ship. for example, I enter 98 feet for the mastheight of all large freighters. Then I estimate the range with the split image, etc, but I do it mainly to replicate what the original captain or fire control officer did. Since most of my shooting is done under 1500 yds, I manually adjust the range once the target gets in close so that I get an accurate representation of the setup on the attack map to confirm the solution. If range is your main problem, you are in good shape. I hope you find this helpful. Joe S

[jazman]

Originally Posted by Joe S

Jazman,

forget about the range, it means nothing. The reason is, once you know the amount of lead, the angle of lead stays the same no matter what the range. I normally set the range with the rangefinder, but I use averages for the type of ship. for example, I enter 98 feet for the mastheight of all large freighters. Then I estimate the range with the split image, etc, but I do it mainly to replicate what the original captain or fire control officer did. Since most of my shooting is done under 1500 yds, I manually adjust the range once the target gets in close so that I get an accurate representation of the setup on the attack map to confirm the solution. If range is your main problem, you are in good shape. I hope you find this helpful. Joe S

Thanks for the advice, I have the O'Kane method down cold. And I worked the trigonometry so I understand why the range doesn't matter. It's when I use the PK for non-O'Kane shooting that I have problems with range.

[Joe S]

Jazman:

Range doesn't matter with either method. If you want, you can pre-set the range for the distance to the target's track at the point of firing. If you are off by a little or a lot it makes no difference. Test the theory in the training mission and let me know what you find. Joe

[Joe S]

Jazman,

If you are having problems with manual tdc it is NOT because of the range estimation. It is more likely error in the speed estimation. a small error in speed estimation will result in a miss except at extemely close range. If you want to improve the stadimeter range finding method, determine the height of the smokestack, which is easier to see than the top of the mast. The top of the mast often dissappears making it impossible to get an accurate fix. If you use the smokestack heigh you should see a big improvement. Joe

[Rockin Robbins]

Originally Posted by jazman

I've tried with the PK all sorts of ways, and I just can't get range right. I hate the Stadimeter and all its works.

Yes, hating the stadimeter is a healthy American thing to do. I'll bet there was some cursing of the stadimeter going on aboard the real subs too.

[XLjedi]

Hmmm... The "O'Kane Method"

For those interested, my nod to O'Kane's tactics were sourced from the war patrols of the Wahoo and Tang books that O'Kane wrote. I think the Wahoo book goes into a little more detail on the firing methods he developed as an XO under Morton.

The one thing he wrote about that stood out in my mind did, in fact, involve overriding the PK. He ordered that a certain targetted bearing be held constant and then he would fire torpedos as points of interest passed the stationary aiming wire. I could quote the chapters and paragraphs but I'd have to go checkout those books again from the library.

However, I do not recall O'Kane EVER writing anything about range not being of importance. I think Robbins memory there is more likely being influenced based on my commentaries on zero-gyro angle shots.

Actually, I don't really care for (at all) the use of a table of lead angles in place of the TDC. To me that just seems silly. ...and to mention it in conjunction with O'Kane probably borders on insulting. The guy was clearly a TDC/PK wiz, and he used the device to its greatest effect. I do not recall O'Kane (in either book) ever referring to a degree lead table as he called his shots.

To the contrary, O'Kane wrote that he drilled continually, both himself and his crew, using a little ship on a Lazy-Susan to get better at estimating AoB. His practice of trying to limit observations to just a few seconds also suggests that he was relying on the PK and other devices to carefully track his prey.

I proposed to mimic SH3 Fast-90 tactics in SH4 in the second "O'Kane Tactics" link of the following thread (and there's a third link there to Robbins followup tutorial). I just liked the idea of giving O'Kane the nod for instilling in me the idea that US sub skippers could override the PK. When I read about that I thought, "Hmmm... Be neat if I could mimic that in SH4."

http://www.subsim.com/radioroom/showthread.php?t=121929

I am pleased at least to see that O'Kane's name has stuck to the tactics described as it pays respect to a great American hero. However, it is starting to get a little too watered down in its presentation and anyone claiming to have "developed it" perhaps comes across as a little boastful. Fast-90 by it's very nature was a method to calibrate the TDC, didn't have anything to do with a lead degree table.

...all I was doing was reapplying what I originally picked up from Wazoo's manual on Fast-90 for SH3. So I wouldn't even go so far as to say that "I develped" or came up with anything special. My original suggestions for applying Fast-90 principles to SH4 did seem to mimic O'Kane to a degree (holding the bearing constant and firing as points passed the wire) so I think he rightly deserved a nod.

Also worth noting that I don't recall ever reading a book on German Uboat tactics that actually used the term "Fast-90", I believe the first and only time I ever saw that term used was in Wazoo's SH3 Manual Targeting Booklet and perhaps scattered here on the SH3 message boards. Someone correct me if you know of a valid historical reference (in fact, I'd love to read the book if it exists).