A WW2 vet gave my son a few books..

[vanjast]

I picked up the one on a british sub, as it has some interesting facts with regard to this area of ops. but this could be on any sea.

- The currents around the islands were heavy, sometimes made it difficult to turn a sub, 'locking' it on it's course, even with full rudder.

- Thermal layers could prevent a sub from diving immediately, delaying the diving time in critical moments. They could also send the sub plummeting down nearly out of control, not to mention forcing the sub to bob up onto the surface ??

- They almost always used ship revs to estimate target speed. The hydrohone guy could identify the engine type and with revs, ship speed.

:)

[Pitts2112]

Fascinating stuff!

I'm just reading "Batfish" and the author describes being inside the Gulfstream current and hitting something that felt as solid as a muddy sea bottom. It turned out it was the bottom of the warm water current where it hit the cold water, and it kept them at that depth, supporting them. He said they could have shut the engines off and just coasted for miles with the current, sitting on the bottom of the thermal layer.

[razark]

- Thermal layers could prevent a sub from diving immediately, delaying the diving time in critical moments. They could also send the sub plummeting down nearly out of control, not to mention forcing the sub to bob up onto the surface ??
Never thought about it, but that makes sense. The different layers are different densities, so it would have an effect on the buoyancy of the boat.

Would be a pain to have to deal with that in the game.

[Task Force]

Never thought about it, but that makes sense. The different layers are different densities, so it would have an effect on the buoyancy of the boat.

Would be a pain to have to deal with that in the game.

As it would probably create a bug makeing is so you cant dive. heh

[razark]

As it would probably create a bug makeing is so you cant dive. heh
No, never. They'd never release something with such a game-breaking bug.

[Schwieger]

Too bad there is not way to implement currents in SH.

[Fish40]

Didn't the great Leo's Living, Breathing Ocean Mod introduce currents to some degree into the game? Man, seems like yesterday:-?

[commandosolo2009]

- They almost always used ship revs to estimate target speed. The hydrohone guy could identify the engine type and with revs, ship speed.

:)

Interesting! I wonder if the speed of the convoy ships be determined this way :06:

[vanjast]

Forgot to mention... It seemed that the brits also had problems with their torps. From what I could make out in the book, only about 25% worked properly.

as an example:
They estimated ship speed the usual way, and from 1000 yards sent a salvo of 6 torps. The second one hit and blew the ships bow - nothing else happened and the ship never sank.

Puzzled by what happened to torps 3 - 6, they sat down for an hour or so working this one out - checking their calculations a few times.. etc.
They worked out that torp 1 was ahead of the bow, and the rest should have hit. According to the author the captain was not happy with the company chosen to manufacture the torps, as they were an appliance manufacturer before the war and did not have the necessary weapons production experience.

Makes sense
:)

[Dogfish40]

I've read in several books that the U-Boats used currents going in and out of Gibraltar strait. It's seems that the shallower water goes one way and the deeper water runs exactly opposite. So they could shut off their engines and go silent, in and out of the strait. Silent.
D40

[Rockin Robbins]

Interesting that book claims that target speed could be derived from engine RPM and type but there is not a single reference during the war as to that method ever being used outside of a general "target is speeding up" or "target is moving slow." I've never seen a speed in knots tied to a hydrophone report in any report made during the war.

There were two thermal conditions that were quite interesting. The first was the usual situation where the top layer was warmer than an underlying cold layer. In this case there was a sometimes wide range of densities where the sub would sink in the lower density warm layer, but float on the higher density layer below. There were a couple of times when submarines were saved by this floating on the layer. They could shut down all engines and work on the sub without worrying about depth control. This condition wasn't really rare.

But the rarer condition is an inversion, where a cold surface layer overlays a warmer layer at depth. They would have to make the sub heavier to sink under the surface, and when it encountered the warm water at the thermocline, the bottom would just drop out. The sub would drop like a rock off a cliff and it took time to pump water out to lighten the sub enough to regain control. It was a rare, but very dangerous situation: a race between the pumps and reaching crush depth.

[vanjast]

Whether this is done to conceal real methods of speed calculation, who knows, but it probably was common knowledge to all involved as no attempt is made to hide it.
The original book looks to have been published in 1947/8 as the foreword has this date, although this edition was published in 2000

I've also seen vague references to this in a few books, but this book has explicit references.

http://www.vanjast.com/IL2Pics/DarkSeasAbove.jpg

:)

[Rip]

I recall reading O'Kane IIRC purchased a metronome to help determine RPMs for more accurate speed measurements.

[Schwieger]

Didn't the great Leo's Living, Breathing Ocean Mod introduce currents to some degree into the game? Man, seems like yesterday:-?

Yea but that is integrated with TMO now and I don't have 1.5.

[Mescator]

I recall reading O'Kane IIRC purchased a metronome to help determine RPMs for more accurate speed measurements.

I can confirm this. He used sonar extensively to establish speeds. In conjunction with other means, of course.

[TorpX]

I picked up the one on a british sub, as it has some interesting facts with regard to this area of ops. but this could be on any sea.

- The currents around the islands were heavy, sometimes made it difficult to turn a sub, 'locking' it on it's course, even with full rudder.

- Thermal layers could prevent a sub from diving immediately, delaying the diving time in critical moments. They could also send the sub plummeting down nearly out of control, not to mention forcing the sub to bob up onto the surface ??

- They almost always used ship revs to estimate target speed. The hydrohone guy could identify the engine type and with revs, ship speed.

:)


I just started reading Thunder Below!, by E.B. Fluckey. They encountered whirlpools, mirage, and strange atmospheric effects, when they were up near the Arctic Circle. Weird Stuff.

[mookiemookie]

I can confirm this. He used sonar extensively to establish speeds. In conjunction with other means, of course.

Indeed. The Fleet Type Submarine manual gave instructions on how to take a proper prop count in order to determine speed.

It, along with these other first person accounts, make it pretty clear that prop count was indeed used to assess target speed regardless of what third person researchers think.

[razark]

Indeed. The Fleet Type Submarine manual gave instructions on how to take a proper prop count in order to determine speed.

It, along with these other first person accounts, make it pretty clear that prop count was indeed used to assess target speed regardless of what third person researchers think.
The sonar stack also included electronics to make it easier to get the prop count. They must have meant for it to be used somehow.

Do any of the sources mention how accurate the speed obtained was?

[mookiemookie]

The sonar stack also included electronics to make it easier to get the prop count. They must have meant for it to be used somehow.

Do any of the sources mention how accurate the speed obtained was?

I can try asking my father. He qual'd on a diesel boat in the late 60's and was an ET. I'll see if the the technology was really that different - my guess is it wasn't.

EDIT: He said, yes, it was done in WW2 but if you wanted any confidence in it you had to pop the scope and make sure you knew what the type of ship you were following was. He said a lot of the tracking of Russian vessels in the Cold War that were done was by hydrophone/sonar, and it was purely through prop count.

[CptChacal]

It gives an estimate of speed. Real speed (useful for attack) depends on the current under the ship. If the ship is making 10 knots against a 3-knot current, its real speed is 7 knots.

[edjcox]

The easy way to increase bouyancy is to blow air into the tanks. This could be done in an emergency but would take surface time to replace the compressed air.

You don't pump water at depth you displace it with air. It's noisy and agiveaway to surface DD Sonar operators. Without the air to displace the volume of water removed the tank would crush like a can...

We gave them some things in exchange ofr the magnetron and other secrets, that included the torpedoe trigger. Being we found them defective and in need of repair does not surprise me that the British Sub fleet did the same. Lend Lease also transfered a number of S Boats tothe the Brits and the Poles along with their Warloads....

[edjcox]

This is an excerpt from WWII Submarine Doctrine manual



Enemy target propeller turn counts are taken whenever possible and are of valuable assistance in estimating target speeds. These should never be used conclusively and must not be used to supplant plotting or other methods of determining target speed for use in solving the torpedo problem. Changes of speed are readily detected by propeller count.

Echo ranging during the conduct of an approach must be used with discretion and with full consideration of many factors. If it is certain that enemy craft lack the equipment necessary to detect transmission from own equipment on the frequencies used, it can then be used with impunity. Under these conditions, when approaching an unscreened target, echo ranging can no doubt be used effectively for checking course and speed, for solution of the torpedo problem, and for own maneuvers in conducting the final stages of the approach. The importance of obtaining a single ping range at about 2500-3000 yards in order to accurately determine target masthead height with which to correct speed data is obvious. Under these same conditions, periscope observations are usually available, but when the masthead height of the target has to be estimated, echo ranges may be more accurate than periscope ranges. If the target is surrounded by a screen, the problem of ranges through wakes left by screens will be difficult. The results must be evaluated before they are used conclusively if a valuable target has made herself subject to attack.
:know:

[vanjast]

It gives an estimate of speed. Real speed (useful for attack) depends on the current under the ship. If the ship is making 10 knots against a 3-knot current, its real speed is 7 knots.
You still have to set ship speed at 10 knots, as you and your torp will also be subject to the current, unless of course the ship is in a very narrow 'current channel' - If you're aware of this channel you'll be lucky.
:)

[vanjast]

We gave them some things in exchange ofr the magnetron and other secrets, that included the torpedoe trigger. Being we found them defective and in need of repair does not surprise me that the British Sub fleet did the same.
This is funny coz from '43 onwards, when this book is based, the brit torpedoes were still dodgey. This may have been due to faulty production methods more than technology, but still the same result.:)

[TorpX]

This is funny coz from '43 onwards, when this book is based, the brit torpedoes were still dodgey. This may have been due to faulty production methods more than technology, but still the same result.:)


O'Kane talks about poor torpedo performance experienced on one of the patrols of the Tang. I don't remember the date. It was so bad, they decided to pull into a quiet inlet, in Japan, at night, so they could observe their runs. An anchored gunboat was there, so they used it for a target. They had to fire 3 or 4 shots to hit it, though it didn't move. IIRC, he blamed manufacturing defects; said torpedo components were made by subcontractors, who had little understanding of what they were making or its function.

The popular conception is of torpedo designs being flawed at the start, and then at a certain date being "fixed", but I think the reality was more complicated. This should not be too big a surprise; torpedos were the most complex pieces of ordnance in their day, comparable to todays "smart weapons".