A WW2 vet gave my son a few books..
 

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.

:)

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.

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

No, never. They'd never release something with such a game-breaking bug.

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

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

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

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
:)

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

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.

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

:)

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

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

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