Torpedo accuracy and circle running.

[WelshZeCorgi]

What exactly is meant when torpedo accuracy is + or - 25%? Like with electric torpedoes. They all seem to swim straight to me. 

Also, were circle running torpedoes also a thing for surface launched torpedoes? They must have, right?

[RAMJB]

I think torpedo accuracy has to do with how easy it is to aim with them for the crew. Not sure, I agree it needs clarification.


Circle running torpedoes were a thing for submarine forces because they almost always were using gyro settings for their torpedoes. Essentially, the submarine wasn't pointed at the aimpoint of the torpedo, so the torpedo had to turn towards the intended firing bearing. It did so with a set of gyros and a set of given instructions for the torpedo. After leaving the torpedo the gyro would know it would have to turn it X degrees either port or starboard to put the torpedo in the correct course, so it did so. This enabled the sub to fire at target solutions well off their bow or stern tubes, even if at a slight loss of accuracy (parallax error induced by the space the torpedo took to turn into it's true intended bearing).

Problem of course is that if by any reason the gyro became stuck, or the torpedo steering malfunctioned, you could end up with a torpedo that instead of turning towards the intended bearing and running straight from there, would circle endlessly. Keeping in mind that at the base of that circle there was the submarine that launched it...well, the results are self-explanatory.


In surface forces, at least in what regards to over-the-water mounts, torpedoes didn't use gyro settings. The mount itself would be trained towards the intended firing beam, and the torpedo would run straight since the second it entered the water. Ditto with underwater torpedo tubes for surface units (those became exceedingly rare after WW1 anyway): the tube itself would be trained towards the intended bearing. No gyro settings needed. Hence, no circle running for those either.

So, at least up to what I know about it, there was never a case of a circle runner for a surface launching unit, while there are several very notable cases of submarines lost to circle runners.

Edited January 10, 2020 by RAMJB

[WelshZeCorgi]

Reading up on the mk 13 US torpedo (the shitty one that needed fixing) circle-running torpedoes can also occur when the torpedo became 'warped'? Not sure what that means exactly, or how a metal construction can warp, not like these things were made of wood. And when manufacturing defects created drag on one side of the torpedo, causing it to turn in the water. 

But yeah, despite these other two reasons why a torpedo, surface or submariner, would circle-run, I've never heard of an example where a DD or TB reported a circle runner. But it never happened? Not even once?

 

[RAMJB]

Warping was a different matter. That kind of thing would cause the torpedo to veer off the intended straight running path at a somewhat constant rate, but quite slowly. If given enough time, enough space (so the torpedo didn't run aground against the coast), and loads of fuel the torpedo wouldn't likely have, that would've resulted in a huge circle with a pretty large radius...not to mention a very long timespan for the torpedo to complete the circle, so if whatever launched it wasn't stationary (which obviously wouldn't be the case), it'd be well out of the way by the time the torpedo would return (Again, if it ever did, because it'd run out of fuel much sooner).


A circle runner was a very different thing. A torpedo fired off with gyro settings had a very tight turning radius and completed it very fast. It's easy to understand why, the faster and the tighter the torpedo turns the "corner" towards it's intended firing path, the least innacuracy will be caused by the parallax efect I Described before. This led to truly small turning radiuses - in the case of the G7 german torpedo, when fired on the 30 knot setting, it would take only 90m of radius to turn into a course 90º off it's fired direction. Now if one of those had a gyro or steering malfunction that locked it in a max rate turn that converted it into a circle runner, then we're talking about a 30 knot torpedo doing a 180m diameter circle. The sub didn't have much time to react to something like that, specially not when in most cases torpedoes were fired while submerged and submarines underwater had top speeds in the 7-8 knots range only. 

BTW the Mk13 was the air-dropped torpedo of the US Navy. Surface forces used the MK15. Submarines used the Mk14 (initially, there were several later marks). Regardless of the distinction, at the very beginning of the pacific war they were all pretty much unreliable junk.


And no, again, surface-dropped torpedoes didn't use gyro settings. They had gyros, but the standard use was to aim them by training the torpedo mount towards the intended bearing, and launching them in straight running without any gyro input. If the torpedo doesn't use the gyros to turn after launch, there's no chance it turns into a circle runner. I can't vouch for it, I can't swear it never happened, but I've never, ever, heard of a circle runner fired by a surface unit, be it TB, DD, cruiser or battleship.

Edited January 10, 2020 by RAMJB

[Fairweather]

HMS Trinidad got hit by her own circling torpedo in 1942- though that was in the Arctic and the torpedo gyro may have frozen.

[akd]

2 hours ago, RAMJB said:

I think torpedo accuracy has to do with how easy it is to aim with them for the crew. Not sure, I agree it needs clarification.


Circle running torpedoes were a thing for submarine forces because they almost always were using gyro settings for their torpedoes. Essentially, the submarine wasn't pointed at the aimpoint of the torpedo, so the torpedo had to turn towards the intended firing bearing. It did so with a set of gyros and a set of given instructions for the torpedo. After leaving the torpedo the gyro would know it would have to turn it X degrees either port or starboard to put the torpedo in the correct course, so it did so. This enabled the sub to fire at target solutions well off their bow or stern tubes, even if at a slight loss of accuracy (parallax error induced by the space the torpedo took to turn into it's true intended bearing).

Problem of course is that if by any reason the gyro became stuck, or the torpedo steering malfunctioned, you could end up with a torpedo that instead of turning towards the intended bearing and running straight from there, would circle endlessly. Keeping in mind that at the base of that circle there was the submarine that launched it...well, the results are self-explanatory.


In surface forces, at least in what regards to over-the-water mounts, torpedoes didn't use gyro settings. The mount itself would be trained towards the intended firing beam, and the torpedo would run straight since the second it entered the water. Ditto with underwater torpedo tubes for surface units (those became exceedingly rare after WW1 anyway): the tube itself would be trained towards the intended bearing. No gyro settings needed. Hence, no circle running for those either.

So, at least up to what I know about it, there was never a case of a circle runner for a surface launching unit, while there are several very notable cases of submarines lost to circle runners.

Brits may have eschewed using gyros on surface torpedos, but the US Navy pursued it and in fact intended that the entire torpedo battery of a destroyer could be launched together and curved ahead at a single target:

https://books.google.com/books?id=YvHGDwAAQBAJ&pg=PT613&lpg=PT613&dq=US+navy+torpedo+gyro+ahead+fire&source=bl&ots=LMyzJrc7Sz&sig=ACfU3U3lRd5x8-s0qn54naTOua-vhvGQVA&hl=en&sa=X&ved=2ahUKEwjhp72Ri_nmAhXLLc0KHSOjA-AQ6AEwDXoECAoQAQ#v=onepage&q=US navy torpedo gyro ahead fire&f=false

Edited January 10, 2020 by akd

[RAMJB]

59 minutes ago, Fairweather said:

HMS Trinidad got hit by her own circling torpedo in 1942- though that was in the Arctic and the torpedo gyro may have frozen.

Goes on to prove that even having read a lot, there's always new stuff to learn every day

 

[RAMJB]

8 minutes ago, akd said:

Brits may have eschewed using gyros on surface torpedos, but the US Navy pursued it and in fact intended that the entire torpedo battery of a destroyer could be launched together and curved ahead at a single target

Brits didn't eschew using gyros - they used them on their torpedos. They just didn't need to bother with setting gyros as it was standard practice to just throw the torpedo at the proper bearing by training the mounts that way. No need to resort to gyros when you just can throw straight runners. But they could do it.

The same as the US. That their torpedoes had gyros and the capability to "curve" doesn't mean it was something used in practice. Which, as far as I know, was not.

Every fleet of the WW2 era had gyros on their modern torpedoes for surface action. Theoretically all had the same capability. But it was far simpler to just throw the torpedo on the true running bearing and leave complexities aside ;). Specially when the US officers knew only too well that their MK15 torpedo couldn't even keep their proper depth (which until 1943, it couldn't), to go on to toy and try to challenge their torpedoes to head in the correct direction by throwing them off-boresight and trusting a gyro to do the turn.

Edited January 10, 2020 by RAMJB

[killjoy1941]

14 minutes ago, RAMJB said:

The same as the US. That their torpedoes had gyros and the capability to "curve" doesn't mean it was something used in practice. Which, as far as I know, was not.

Every fleet of the WW2 era had gyros on their modern torpedoes for surface action. Theoretically all had the same capability. But it was far simpler to just throw the torpedo on the true running bearing and leave complexities aside ;). Specially when the US officers knew only too well that their MK15 torpedo couldn't even keep their proper depth (which until 1943, it couldn't), to go on to toy and try to challenge their torpedoes to head in the correct direction by throwing them off-boresight and trusting a gyro to do the turn.

Correct. I know of no primary source which indicates torpedo gyros were ever actually engaged on US surface ships. As far as I can determine, gyro use wasn't even part of the training for the torpedo mount crews, at least other than an "oh, by the way, the torpedoes have gyros" kind of way. 

Crenshaw spends quite a bit of time discussing the shortcomings of the Mk15 at the end of his book (South Pacific Destroyer), which is still the best primary source for the actual performance of the Mk15. It wasn't that the Mk15 couldn't keep depth, but that it consistently ran far deeper than set. The US started scoring torpedo hits when captains began ordering torpedoes set to the minimum allowable depth.

[akd]

Gyro angles were certainly used on MTBs, and I'd be very surprised to learn they were never used to control spreads of torpedoes from other surface combatants.  You are taking the historical determinism approach (e.g. this didn't happen in WWII so it should simply be excluded entirely), where I think it is better to look at the possibilities of the technology and game it out, because the circumstances of your war might be radically different than what developed historically.  If using gyro angles incurred both advantages and disadvantages, model both and let us game it out.

Quote

27B3. Methods of firing

The two methods of firing torpedoes are: (1) straight fire, and (2) curved fire. In both methods, the torpedoes are normally fired in a spread, produced by setting small angular offsets onto the torpedo gyro mechanism of the individual torpedoes. Curved fire is accomplished by setting an additional uniform offset angle on all the torpedoes in the mount to the angle it is desired for the torpedoes to turn right or left after being launched. Torpedo-tube mounts have limited sectors in which torpedoes can be launched without striking some part of the firing ship’s structure. It is therefore frequently necessary to use curved fire to unmask the torpedo battery if the tactical situation does not permit changing course. The two methods of firing torpedoes are shown in figure 27B4, along with further elements of the torpedo control problem.

https://eugeneleeslover.com/USNAVY/CHAPTER-27-B.html

https://maritime.org/doc/pt/doctrine/part4.htm

I'm also fairly certain that not all submerged tubes were trainable and use of gyro angles was the only means of aiming these.

Edited January 10, 2020 by akd

[akd]

3 hours ago, akd said:

Torpedo-tube mounts have limited sectors in which torpedoes can be launched without striking some part of the firing ship’s structure. It is therefore frequently necessary to use curved fire to unmask the torpedo battery if the tactical situation does not permit changing course.

It is interesting to note that the above seems to be a problem we are experiencing in game, where possibly only certain tubes of a multiple launcher are able to fire at a given moment, messing up the ability to fire spreads.

Also, here is a good discussion on fixed tubes:

https://www.tapatalk.com/groups/alltheworldsbattlecruisers/submerged-torpedo-tubes-on-battleships-t768.html

Edited January 10, 2020 by akd

[disc]

The determinism approach is especially inappropriate given that we know that gyro setters were present on US surface ships, and that all US submarines post-1925 had gyro setters. By 1941 continuous setters were installed.

The manual for the Mark 14 surface-ship launcher (ie the one used on like 300 destroyers) explicitly shows both the setter and a dedicated crewman to enter gyro settings.

Also I'm not sure any general history would mention gyro setting except in the context of failures....

 

Edit: The 1947 torpedo fire control equipment (destroyers) manual describes gyro control pretty well. It does not describe any outstanding postwar issues with angling. Apparently there was even a specific setting to deal with latitude of the Earth.

Links to both:

https://maritime.org/doc/destroyer/ddtubes/index.htm
https://maritime.org/doc/destroyer/ddfc/index.htm

Edited January 10, 2020 by disc