[REL] We Dive at Dawn

[Hitman]

We'll need zero Gyro Angle torpedoes (Locked instead of limited to 15º) to go along with this mod

I have figured out how to get both the periscope lead angle and alternatively the moment of shooting. For the first one, you need to enter all target data into the TDC and NOT start the position keeper. Once the data are fed, the difference in degrees between the arrow in the lower dial (Gyro Angle arrow) and the line of sight (upper part of the dial) is the necessary lead angle, so you just need to turn your scope that many degrees in direction to your target and shoot when it crosses the periscope line. For the second, you would simply follow the target until the arrow matches the bow of the ship silhouette on it, at that moment the necessary Gyro Angle is zero and your torpedo will find the target.

Gotta love how frigging challenging it was to hit anything at all with those WW1 methods

[Forensicman101]

As long as you are attacking the target so that your torpedoes are striking at 90 degrees off the target's bow the calcuations are quite straightforward with a bit of basic trigonometry (I've included a table for this in my "Double Whammy" document). e.g. a 45.5 kt torpedo being fired at a 12 kt target would have to be fired when the target was approximately 15 (actually 14.8) degrees off the submarine's bow in such circumstances. As always, the trick is to remember that you're not firing at a target, but at where the target will be when your torpedo arrives at the same location. I guess the real difficulties arise when the point of intercept is greater or less than 90 degrees. I suppose that's where the fruit machine comes into play.

[keltos01]

[QUOTE=Hitman;1559430]We'll need zero Gyro Angle torpedoes (Locked instead of limited to 15º) to go along with this mod
not a problem !!!

I have figured out how to get both the periscope lead angle and alternatively the moment of shooting. For the first one, you need to enter all target data into the TDC and NOT start the position keeper. Once the data are fed, the difference in degrees between the arrow in the lower dial (Gyro Angle arrow) and the line of sight (upper part of the dial) is the necessary lead angle, so you just need to turn your scope that many degrees in direction to your target and shoot when it crosses the periscope line. For the second, you would simply follow the target until the arrow matches the bow of the ship silhouette on it, at that moment the necessary Gyro Angle is zero and your torpedo will find the target.

Gotta love how frigging challenging it was to hit anything at all with those WW1 methods

I'll quote "submarine commander" by rear admiral Ben Bryant on that tomorrow..

sheer luck and a seaman's eye was what he said !

keltos

[Hitman]

I guess the real difficulties arise when the point of intercept is greater or less than 90 degrees. I suppose that's where the fruit machine comes into play.

Exactly. And to be more specific, the british captains, like the US ones, favoured a track angle of 110 degrees (Better ask Rockin Robins why, I don't remember right now) and usually asked the TDC operator to provide an attack course for that track angle.

[keltos01]

the British torpedoes could be set at either 0 or 90° angle, nothing between.

unfortunately I don't think SH4 can support two set giro angles, so we'll have to go with 0° only...

keltos

[Hitman]

It could support both GA, but I have never seen a record of a 90º shot, they did the vast majority as 0º degrees shots. There are several reasons why you would do that, but the main one is that the lack of parallax (convergence) means that distance to target is largely irrelevant, something that eliminates a variable from the problem and makes shooting easier.

[keltos01]

Originally Posted by Hitman

It could support both GA, but I have never seen a record of a 90º shot, they did the vast majority as 0º degrees shots. There are several reasons why you would do that, but the main one is that the lack of parallax (convergence) means that distance to target is largely irrelevant, something that eliminates a variable from the problem and makes shooting easier.

I read in my book that they sometimes tried the 90° shot too...


keltos

[Forensicman101]

If you set yourself up at 90 degrees to the target's course & fire you torpedoes at zero gyro when the target is at the appropriate angle from your bow you can achieve some quite high hit rates. As noted by Hitman, range becomes irrelevant, so the only factors to consider are the speed of the target and the speed of your torpedo. All of that can be put into a simple table which can be consulted in a couple of seconds to give you the angle from your bow that the torpedo needs to be fired at (basic trig'). If you fire your first torpedo at low speed and the second at high speed you can achieve a Double Whammy.

Given that early TDCs could sometimes malfunction due to incorrect data input or mechanical / electrical problems, you can see some sense in the simple approach.

[joegrundman]

Originally Posted by Hitman

Exactly. And to be more specific, the british captains, like the US ones, favoured a track angle of 110 degrees (Better ask Rockin Robins why, I don't remember right now) and usually asked the TDC operator to provide an attack course for that track angle.

At 110 degrees (or thereabout, actually it is a function of target and torp speed), the rate of change of target AOB is slowest.

[joegrundman]

Originally Posted by keltos01

I read in my book that they sometimes tried the 90° shot too...


keltos

Didn't the later war MkVIII have full variable gyro?

[keltos01]

http://www.flickr.com/photos/anguskirk/4878474817/



Uploaded with ImageShack.us

http://www.militaryimages.net/photop...php/photo/1607

Originally Posted by joegrundman

Didn't the later war MkVIII have full variable gyro?

http://www.navweaps.com/Weapons/WTBR_WWII.htm

http://en.wikipedia.org/wiki/British...inch_Mark_VIII


keltos

[keltos01]

loading torp on a T








a rare view !

HMS/M Safari photo of destroyer hunting the sub by Capt Bryant



torpedoed tanker


http://adjunct.diodon349.com/photopoint/0025/0022.jpg

[joegrundman]

Originally Posted by keltos01

http://www.navweaps.com/Weapons/WTBR_WWII.htm

http://en.wikipedia.org/wiki/British...inch_Mark_VIII


keltos

sorry, i didn't see that those links referred to gyro angles at all

[keltos01]

that data on gyros is hard to find I read it in a book I'm currently re reading.

Merry Xmas

keltos

[keltos01]

Ben Bryant retired from active submarine duty in 43, so his book though very good, only goes so far.

p120 he uses the ninety bender to get a ship that is on a parallel course

"the column were 3 cables or 600 yards apart...the sights came on and we fired at the leading ship of the port column, angled 90° left."


he actually got this ship though at the time he thought hed' missed, but was already busy being depth charged.

nothing about the gyro going all the way like the american one. they were too close to one column to fire at 0° angle so they chose another target and set the torps at 90°.


they also used a slide rule to calculate the range, thus more prone to mistakes :

p 140 : " we steadied on the firing course and I passed the number of divisions on the periscope gradicule from which the attack team could calculate the range on a slide rule. The slide rule did not compete direct with such a small target as a U-Boat and you had to multiply or divide according to the technique employed. The slide-rule operator made a mistake, which was easy to do, and multiplied by two instead of dividing, and announced the range as about 3200 yards. I spotted the mistake but did not remark upon it as the sights were just coming on, I just mentally noted that hte range was 800 yards."

the trim officer then let the boat go under periscope depth as he thought he had time to trim the boat better, and they missed the firing opportunity on the U-Boat...

keltos