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

[marcelo_malara]

Hi All,

On these figures, Rio Tercero subtends only 0.22 of a degree 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".

wadinga

Hi Wadinga. Sorry but your numbers are wrong here. One degree is 17 m at 1000 m, so it would be 73 m at 4300 m, the whole ship would be about 2 degrees long.

[dunmunro]

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.

From reading the KTB, the range at the moment of firing was ~2000m. The run time is the range at the moment of firing plus the target's movement after the torpedo is fired. The FC computer needs the range at moment of firing, along with the speed and course of the target to compute the firing angle required (along with the computed run time).

[marcelo_malara]

Nooo, do you think that an 11 knot ship would sail 2300 m in 4 minutes? Moreover, look at the geometry of the attack, there is no way range could have changed so much during runtime.

[marcelo_malara]

FC computer only needs:

-target bearing
-target speed
-angle on the bow, inclination or target aspect angle, anyway you call it

Optionally:

-for large gyro angle target range
-target length for dispersion

[dunmunro]

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:

?

These numbers have to be taken with a grain of salt, as the KM was firing at much larger targets, typically against unescorted or poorly escorted large displacement ships, whereas the RN was typically attacking small displacement, heavily escorted ships.

FWIW:
RN (and Allied non USN) subs scored

...1363 hits out of 3220 attacks (42.3%) and 1040 ships were sunk out of 5121 torpedoes fired (20.3%). In the USN 1314 sinkings were achieved by angled fire with 14,748 torpedoes (8.9%).

Compton-Hall, The Underwater War 1939-45.

[dunmunro]

Nooo, do you think that an 11 knot ship would sail 2300 m in 4 minutes? Moreover, look at the geometry of the attack, there is no way range could have changed so much during runtime.

This is the KTB entry:

Three fan from tube I, II, IV fire! Shooting data: Bow right, target angle 80°, speed 11 knots, range = 2000 meters, spread angle 2, depth 3 meters, aim point center.
Hit after 4 minutes 43 seconds = 4350 meters. Hit center. High detonation cloud, afterwards white smoke from the boiler room. Ran closer. Steamer does not even have a flag, additionally no special markings. Armament not recognized. Steamer sets no boats out, but rather slowly turns towards me. Is it a trap? I had better give him a coup de grace. Except for the smoke no effect from the shot is noticed.

My emphasis.

[wadinga]

Hi Marcelo,

I edited my error but you were much too quick for me. I entered the beam not the length. The ship was 1.6 degrees but with 2 degrees between shots it was a lucky hit - was it the left,middle or right which hit? The other two were insurance to cover the inherent errors.

-target bearing
-target speed
-angle on the bow, inclination or target aspect angle, anyway you call it

One can be measured the others are mere estimates. The estimates generate the future position to which the torpedo must travel. If the torpedo arrives too early or too late it's a miss.

All the best

wadinga

[marcelo_malara]

This is the KTB entry:

Three fan from tube I, II, IV fire! Shooting data: Bow right, target angle 80°, speed 11 knots, range = 2000 meters, spread angle 2, depth 3 meters, aim point center.
Hit after 4 minutes 43 seconds = 4350 meters. Hit center. High detonation cloud, afterwards white smoke from the boiler room. Ran closer. Steamer does not even have a flag, additionally no special markings. Armament not recognized. Steamer sets no boats out, but rather slowly turns towards me. Is it a trap? I had better give him a coup de grace. Except for the smoke no effect from the shot is noticed.

My emphasis.

Sorry, I have already explained the 2000 m question. The distance at the moment of firing was even greater than 4300 m, if you look at the plot I posted for a target impact angle of almost 90° the closest the target would be is at the very moment of impact. You can crudely measure with a ruler directly on the screen (if you want).

[marcelo_malara]

Hi Marcelo,

-target bearing
-target speed
-angle on the bow, inclination or target aspect angle, anyway you call it

One can be measured the others are mere estimates. The estimates generate the future position to which the torpedo must travel. If the torpedo arrives too early or too late it's a miss.


[/quote]

Yes, you are right, only the bearing can be measured, the other are estimates. With time, the skipper would make a first estimate and then track the target for some time, if his estimates were right the position keeper would produce the same target bearing as he could observe with the periscope,

[dunmunro]

This is the KTB entry:

Three fan from tube I, II, IV fire! Shooting data: Bow right, target angle 80°, speed 11 knots, range = 2000 meters, spread angle 2, depth 3 meters, aim point center.
Hit after 4 minutes 43 seconds = 4350 meters. Hit center. High detonation cloud, afterwards white smoke from the boiler room. Ran closer. Steamer does not even have a flag, additionally no special markings. Armament not recognized. Steamer sets no boats out, but rather slowly turns towards me. Is it a trap? I had better give him a coup de grace. Except for the smoke no effect from the shot is noticed.

My emphasis.

Sorry, I have already explained the 2000 m question. The distance at the moment of firing was even greater than 4300 m, if you look at the plot I posted for a target impact angle of almost 90° the closest the target would be is at the very moment of impact. You can crudely measure with a ruler directly on the screen (if you want).

That doesn't make sense. What does make sense is that target angle = 80deg actually states that the target is moving rapidly away from the Uboat.

I have the original KTB, run time 4 min 43 sec, that for a 30 kt torpedo means 4300 m.

The diagram that you posted cannot have a range of 2000m anywhere in it when the torpedo run time (and consequent range) = 4350m

[marcelo_malara]

That doesn't make sense. What does make sense is that target angle = 80deg actually states that the target is moving rapidly away from the Uboat.

Could you draw the geometry of this and explain how an angle on the bow/inclination/target aspect angle of 80° means a retiring vehicle?

Regards

[Byron Angel]

UNITED STATES SUBMARINE OPERATIONS IN WORLD WAR II, Theodore Roscoe, page 54
"Throughout the war the percentage of hits was more or less constant for track angles between 60deg and 120deg and ranges between 1,000 and 3,000 yards. Within the region the scored hits averaged 36%. The percentage of hits was independent of the gyro angle for values of the gyro angle between zero and 40deg."

The USN's Arma Mk3 TDC was an excellent WW2 torpedo fire control system. Many argue that a valid argument can be made that it was the finest such device of the war.

The Mark XIV torpedo, not so much. Multiple design flaws plagued it until 1943 - bad depth sensor design, badly designed contact fuze, bad magnetic influence detonator, terrible bureaucratic infighting.

Byron

[dunmunro]

That doesn't make sense. What does make sense is that target angle = 80deg actually states that the target is moving rapidly away from the Uboat.

Could you draw the geometry of this and explain how an angle on the bow/inclination/target aspect angle of 80° means a retiring vehicle?

Regards

Again, this is the KTB entry:

Three fan from tube I, II, IV fire! Shooting data: Bow right, target angle 80°, speed 11 knots, range = 2000 meters, spread angle 2, depth 3 meters, aim point center.
Hit after 4 minutes 43 seconds = 4350 meters. Hit center. High detonation cloud, afterwards white smoke from the boiler room. Ran closer. Steamer does not even have a flag, additionally no special markings. Armament not recognized. Steamer sets no boats out, but rather slowly turns towards me. Is it a trap? I had better give him a coup de grace. Except for the smoke no effect from the shot is noticed.

If the (approximate) range at the moment of firing was 2000 meters, then the range had to open, and the only way that can happen is if the target is moving away from the u-boat. We know that the range at the moment of impact was 4350 meters, so the KTB cannot be referring to range as the run time of the torpedoes. I don't need to draw a diagram for anyone to visualize this.

The KTB states: "...range = 2000 meters..." I didn't make that statement, the skipper of the uboat did.

[dunmunro]

UNITED STATES SUBMARINE OPERATIONS IN WORLD WAR II, Theodore Roscoe, page 54
"Throughout the war the percentage of hits was more or less constant for track angles between 60deg and 120deg and ranges between 1,000 and 3,000 yards. Within the region the scored hits averaged 36%. The percentage of hits was independent of the gyro angle for values of the gyro angle between zero and 40deg."

The USN's Arma Mk3 TDC was an excellent WW2 torpedo fire control system. Many argue that a valid argument can be made that it was the finest such device of the war.

The Mark XIV torpedo, not so much. Multiple design flaws plagued it until 1943 - bad depth sensor design, badly designed contact fuze, bad magnetic influence detonator, terrible bureaucratic infighting.

Byron

I'm certain that the RN thought the TDC was excellent as well, but the fact remains that if USN subs had been equipped with RN torpedoes and the RN STD, that their torpedo hit rate would have been much higher than it was, for at least the first two years of the USN's entry into the Pacific war.

[marcelo_malara]

The USN's Arma Mk3 TDC was an excellent WW2 torpedo fire control system. Many argue that a valid argument can be made that it was the finest such device of the war.

The Mark XIV torpedo, not so much. Multiple design flaws plagued it until 1943 - bad depth sensor design, badly designed contact fuze, bad magnetic influence detonator, terrible bureaucratic infighting.

Byron

If you can get the book:

https://www.amazon.com/Fleet-Submarine- ... 0974304530

Without doubt it was a complex and fine piece of equipment, having even the capability of blind firing basing the target info on sonar alone (don´t know how many times this was actually used).