British submarines' torpedo hits compared to German u-boats'

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Re: British submarines' torpedo hits compared to German u-boats'

Post by dunmunro »

marcelo_malara wrote: Thu Jun 16, 2022 10:40 pm The ability to fire without pointing the sub is important in many cases. For example if you are following a target from its beam, you can do this for the time you like, verifying continually the target plot and the fire solution. If you can not angle the gyro you must continually approach the target to keep a fire solution for some time. If you use the 90° degree gyro the sub will be getting away of the target for the fire solution to be valid for some time.

Moreover, that the British engineers could not compute a salvo with gyro (which needs to solve mechanically a non linear equation), while Americans and Germans did, may imply that the computer was a little behind existing technology and less reliable than the others´powers.

Regards
It's actually relatively easy to compute the firing angles but a lot harder to ensure that the torpedo carries out the requested gyro angle turn accurately. Both the USN and KM had real problems developing reliable torpedoes and part of their reliability problems (especially for the USN) involved problems with gyro angling.

The RN had a reliable torpedo and an accurate FC system from the 1st day of the war whereas it took the USN more than two years after their entry into the war to develop a reliable and accurate torpedo. USN subs fitted with RN torpedoes and RN FC would have been far more accurate than historically was the case.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

For a no gyro firing it is a simple trigonometric calculation, composed of torpedo and target speed, target bearing and angle on the bow. For a gyro firing it is not so easy as it seems. To the above the computer needs also to take into account the turning radius of the torpedo and, most important, the range, that in a no gyro shot takes no place. As the range is difficult to assess without a rangefinder, most skippers avoided using gyros whenever possible.

A question that comes to my mind is, how was a spread fired from a RN sub? In German and USN subs it was achieved by giving each torpedo a slight change in the gyro, about 1°, so each torpedo in a salvo would take a course 1° +- than its neighbor. Only way to launch a spread (if you can not angle the gyro) is firing each torpedo while turning slowly. That´s not good.
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Re: British submarines' torpedo hits compared to German u-boats'

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marcelo_malara wrote: Thu Jun 16, 2022 11:39 pm For a no gyro firing it is a simple trigonometric calculation, composed of torpedo and target speed, target bearing and angle on the bow. For a gyro firing it is not so easy as it seems. To the above the computer needs also to take into account the turning radius of the torpedo and, most important, the range, that in a no gyro shot takes no place. As the range is difficult to assess without a rangefinder, most skippers avoided using gyros whenever possible.

A question that comes to my mind is, how was a spread fired from a RN sub? In German and USN subs it was achieved by giving each torpedo a slight change in the gyro, about 1°, so each torpedo in a salvo would take a course 1° +- than its neighbor. Only way to launch a spread (if you can not angle the gyro) is firing each torpedo while turning slowly. That´s not good.
Off hand, I'd say that you only had to introduce a few seconds delay between firing each torpedo, but I'd have to do more research to know if that's true. However, it seems likely based upon RN surface ship torpedo firing.
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Re: British submarines' torpedo hits compared to German u-boats'

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dunmunro wrote: Fri Jun 17, 2022 2:04 am
marcelo_malara wrote: Thu Jun 16, 2022 11:39 pm For a no gyro firing it is a simple trigonometric calculation, composed of torpedo and target speed, target bearing and angle on the bow. For a gyro firing it is not so easy as it seems. To the above the computer needs also to take into account the turning radius of the torpedo and, most important, the range, that in a no gyro shot takes no place. As the range is difficult to assess without a rangefinder, most skippers avoided using gyros whenever possible.

A question that comes to my mind is, how was a spread fired from a RN sub? In German and USN subs it was achieved by giving each torpedo a slight change in the gyro, about 1°, so each torpedo in a salvo would take a course 1° +- than its neighbor. Only way to launch a spread (if you can not angle the gyro) is firing each torpedo while turning slowly. That´s not good.
Off hand, I'd say that you only had to introduce a few seconds delay between firing each torpedo, but I'd have to do more research to know if that's true. However, it seems likely based upon RN surface ship torpedo firing.

The seconds interval is standard practice, it is done so the sub would no loose so much weight at once and risk breaking surface. But if during the interval you don´t change course the next torpedo would take the same course as the previous one.
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Re: British submarines' torpedo hits compared to German u-boats'

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marcelo_malara wrote: Fri Jun 17, 2022 3:19 am
dunmunro wrote: Fri Jun 17, 2022 2:04 am
marcelo_malara wrote: Thu Jun 16, 2022 11:39 pm For a no gyro firing it is a simple trigonometric calculation, composed of torpedo and target speed, target bearing and angle on the bow. For a gyro firing it is not so easy as it seems. To the above the computer needs also to take into account the turning radius of the torpedo and, most important, the range, that in a no gyro shot takes no place. As the range is difficult to assess without a rangefinder, most skippers avoided using gyros whenever possible.

A question that comes to my mind is, how was a spread fired from a RN sub? In German and USN subs it was achieved by giving each torpedo a slight change in the gyro, about 1°, so each torpedo in a salvo would take a course 1° +- than its neighbor. Only way to launch a spread (if you can not angle the gyro) is firing each torpedo while turning slowly. That´s not good.
Off hand, I'd say that you only had to introduce a few seconds delay between firing each torpedo, but I'd have to do more research to know if that's true. However, it seems likely based upon RN surface ship torpedo firing.

The seconds interval is standard practice, it is done so the sub would no loose so much weight at once and risk breaking surface. But if during the interval you don´t change course the next torpedo would take the same course as the previous one.
Yes, but as the target is moving, the torpedoes are still spread, as seen by the target:


6
02. TYPES OF SPREAD:

(a) Divergent Spread

A divergent spread is a spread in which the torpedoes of a salvo intersect the target's track at different points along the target's length and at different torpedo track angles. This type of spread is difficult to avoid because of its fan-shaped pattern. (Diagram A, Plate XV).

(b) Longitudinal Spread

A longitudinal spread is the spread obtained by firing a salvo of torpedoes along identical torpedo tracks. Torpedo #1 hits the target at A, #2 at B, and #3 at C, due to movement of target across the identical track of the torpedoes. It is a simple type of spread, having the disadvantage that the target which can avoid one torpedo track undoubtedly can avoid the others which are following in the wake of the first. (Diagram B, Plate XV).

(c) There are many different types of spreads which may be used. During the war numerous "gadgets" were designed and used in setting spreads. No matter what spread is used it should embody certain basic elements. These are:

1. Target length
2. Torpedo track
3. Torpedo run
4. Coverage[
http://archive.hnsa.org/doc/attack/index.htm#chap06
Of course there's nothing particularly difficult about have the sub make a constant rate of turn during the firing sequence.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

Well, that would be a reason for the (may be) better German performance, an angled spread is more difficult to avoid.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

I would like to see a Report of Proceedings of a WWII RN sub, do we have something of this?
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Re: British submarines' torpedo hits compared to German u-boats'

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marcelo_malara wrote: Fri Jun 17, 2022 5:27 pm I would like to see a Report of Proceedings of a WWII RN sub, do we have something of this?
Only a few:

I've attached an image file of HM/S Vigorous' 4th war patrol (Sept-Oct 1944) in the MTO:
HMS_Vigorous_4thPatrol.jpg
(203.97 KiB) Not downloaded yet
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

Thanks!

At first sight some numbers don´t look good, a salvo of 4 torpedoes at 1000 yards on a 6 kt target and hitting with only one is, I must say,...poor. It seems that the technique was firing the torpedoes as the selected parts of the ship were coming into the periscope pip, so the long delays between them. Do you know the term "D.A. used"? It seems to be the lag angle between the periscope bearing and the bow/course of the sub.

The British contrast with the German technique, that was firing always (as far as I have seen in the reports) using the computer, with short delays (2 or 3 seconds) between torpedoes, and giving each a slight different course setting the gyros.

This is illustrated in this plot of the attack of the Argentine cargo ship Rio Tercero in 1942.

Image
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Re: British submarines' torpedo hits compared to German u-boats'

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marcelo_malara wrote: Sat Jun 18, 2022 3:21 pm Thanks!

At first sight some numbers don´t look good, a salvo of 4 torpedoes at 1000 yards on a 6 kt target and hitting with only one is, I must say,...poor. It seems that the technique was firing the torpedoes as the selected parts of the ship were coming into the periscope pip, so the long delays between them. Do you know the term "D.A. used"? It seems to be the lag angle between the periscope bearing and the bow/course of the sub.

The British contrast with the German technique, that was firing always (as far as I have seen in the reports) using the computer, with short delays (2 or 3 seconds) between torpedoes, and giving each a slight different course setting the gyros.

This is illustrated in this plot of the attack of the Argentine cargo ship Rio Tercero in 1942.

Image
As I stated the RN subs were operating in a 'target poor' environment, where a small (~1000 ton) ship was an exceptional target as you can read from the 3 other torpedo attacks.

This is what Uboat.net has to say:
At 12.34 hours on 22 June 1942 the unescorted and neutral Rio Tercero was hit by one of three torpedoes from U-202 and sank slowly about 120 miles off New York. Linder reported that the ship displayed no neutrality markings and was recognized as Argentinian only after the attack when questioning the survivors.
https://uboat.net/allies/merchants/ships/1836.html
Hitting a larger ship with one of 3 torpedoes doesn't seem illustrative of superior technique.

I suspect that D.A. might mean 'Director Angle'.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

Director angle, yes, I should have known, as the RN computer was so called.

In the case of the Rio Tercero (nothing special with this case except that it was a neutral vessel) the shot was at 4300 m and was steaming at 11 knots, it may rank high between the longest ranged torpedo hits in the war. The running time was 4 min 43 sec.
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Re: British submarines' torpedo hits compared to German u-boats'

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marcelo_malara wrote: Sat Jun 18, 2022 6:09 pm Director angle, yes, I should have known, as the RN computer was so called.

In the case of the Rio Tercero (nothing special with this case except that it was a neutral vessel) the shot was at 4300 m and was steaming at 11 knots, it may rank high between the longest ranged torpedo hits in the war. The running time was 4 min 43 sec.
The range at the moment of firing was ~2000 meters.

On 23 Feb HM/SM Trident blew the stern off of Prinz Eugen, with one of 3 torpedoes fired at ~2000 yds. I don't know the run time.

In April 1940 Truant hit Karlsruhe with one of 10 torpedoes fired at 4500 yds. It's hard to work out the run time unless it's stated or the geometry of the attack is known.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by marcelo_malara »

A crude estimate:

Germany fired:

7000 G7e
2300 G7a
640 T5

Total 9940

(Naval weapons of WWII)

Ship sunk with them:

2673

(https://uboat.net/special/analysis.htm)

Effectivity

27%


UK fired:

5121 (presumably all Mk VIII)

(Naval weapons of WWII)

Ship sunk with them:

?
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Re: British submarines' torpedo hits compared to German u-boats'

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dunmunro wrote: Sat Jun 18, 2022 6:42 pm
marcelo_malara wrote: Sat Jun 18, 2022 6:09 pm

In the case of the Rio Tercero (nothing special with this case except that it was a neutral vessel) the shot was at 4300 m and was steaming at 11 knots, it may rank high between the longest ranged torpedo hits in the war. The running time was 4 min 43 sec.
The range at the moment of firing was ~2000 meters.

No, that is incorrect. I have the original KTB, run time 4 min 43 sec, that for a 30 kt torpedo means 4300 m.

The 2000 m needs an explanation. As I said range plays no part in the torpedo equation, except for very large gyro angles. As the Germans attacks were mostly (or may be all) made by computer, and the computer recalculated continually the range, If the actual range (in this case +4000 m) was entered in the computer, the risk was that the computer would calculate a range at the moment of impact in excess of the torpedo range, and so disabled the launching. So, for a small angle gyro salvo, as in this case, a smaller range was entered in the computer.
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Re: British submarines' torpedo hits compared to German u-boats'

Post by wadinga »

Hi All,

I have suggested already the element of luck/skill in getting a good firing solution when target speed/course are actually unknown and only estimated from occasional periscope viewings. On these figures, Rio Tercero subtends only 1.6 degrees at 4300m (if beam on to the U-boat) so spreading by 2 whole degrees between shots as shown indicates how much luck was involved in this circumstance. I am sure I have read an account saying U-boat commanders frequently overrode a no-fire indication from their computer, as it was "worth a try" when the machine actually said you're wasting your time (and torpedoes). Of course, running out of torpedoes is a good reason for going home to the bars and other "nightlife". :cool:

Director angle is analogous to deflection in gunnery, firing on an azimuth ahead of the target so the weapon arrives at the same point at the same time as the target. I suspect the anti-sophistication/pragmatic bias of the Royal Navy thought the so-called "Fruit Machine" was adequate. Range estimation consisted of either comparing vertical graticule marks with vessel mast height, or a using very short baseline coincidence rangefinder mounted in the periscope. Speed estimation was based on bow wave and bearing change relative to own movement. Bearing would come from the periscope relative to submarine's head wherever it was. Manual plotting was sometimes used to try and derive values based on own course and speed.

Having a more complicated computer may be pointless if the entered data is incorrect in the first place. Of course point blank shooting makes things much easier. Many German successes were scored from night surface attacks on (sometimes within) convoys before radar, or against unescorted merchant ships where a single shot from a few hundred yards was an easy kill.

We have already considered the large number of U-boats and the corresponding large number of targets compared with the paucity of HM submarines and their targets. Apparently 73% of German shots either missed or failed to sink their targets which just goes to show how difficult it was.

Turning a torpedo is a risky business, it can easily lose its sense of its verticality. Gyro controlled rudders must remain vertical and depth control ones horizontal otherwise circling torpedo syndrome can set in. Better to let it run hot, straight and normal.

All the best

wadinga
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