Calculation tools on WWII subs

[Raven Morpheus]

Hi all

This is more of a general question regarding WWII subs, but I couldn't find a place to put it.

My mental arithmetic has never been great, so I usually use a calculator. However, obviously back in WWII they never had such luxuries.

I'm thinking of when for example a skipper had to calculate things like the speed of a ship based on the known length and how long it takes the ships to cross the periscope crosshairs (i.e. length/time x 1.94).


So, what did they use, did they just use a pen and paper or did they have some sort of tool (like a slide rule?)?


TIA

[razark]

Slide rule.

Specifically: http://maritime.org/doc/attackfinder/index.htm
Also: http://www.subsim.com/radioroom/showthread.php?t=106923

Any slide rule with a sin scale can be used, though.
http://www.subsim.com/radioroom/showthread.php?t=112765

[Rockin Robbins]

Originally Posted by Raven Morpheus

Hi all

This is more of a general question regarding WWII subs, but I couldn't find a place to put it.

My mental arithmetic has never been great, so I usually use a calculator. However, obviously back in WWII they never had such luxuries.

I'm thinking of when for example a skipper had to calculate things like the speed of a ship based on the known length and how long it takes the ships to cross the periscope crosshairs (i.e. length/time x 1.94).


So, what did they use, did they just use a pen and paper or did they have some sort of tool (like a slide rule?)?


TIA

They NEVER NEVER NEVER calculated a single target's speed using the length by the wire method, neither in the Atlantic nor Pacific, neither US, British, French, Dutch, German, Italian, Brazilian nor any other sub.

That is just a gamey, made-up method with no plausibility whatever. Since it was never done no calculators were ever designed for it.

It has two absolutely fatal errors. First, it guarantees a large percentage error in speed calculated due to the extremely short timing. The shorter the time between the two datum points the larger the error. It's difficult to conceive a method with more inherent error, calculating only over at single ship length. That alone disqualifies it from any consideration at all.

But secondly, it (as does the American stadimeter method) absolutely requires proper identification of the target. During the war less than half the targets were identified properly, resulting in target length errors between plus and minus 100%! What does THAT do to your speed measurement? Yeah, we're accurate to within a factor of four! Ever wonder why American subs, with a technologically superior TDC had fewer hits per torpedo than the Germans? It was because the standard stadimeter method of shooting required target ID. The Germans didn't care about target ID because it was not part of the shooting process. American skippers, like Dick O'Kane, who used constant bearing techniques rather than conventional US tactics, also hit a much higher percentage of targets. Why? Target ID wasn't necessary.

[Aktungbby]

Originally Posted by Raven Morpheus

Hi all


I'm thinking of when for example a skipper had to calculate things like the speed of a ship based on the known length and how long it takes the ships to cross the periscope crosshairs (i.e. length/time x 1.94).


So, what did they use, did they just use a pen and paper or did they have some sort of tool (like a slide rule?)?


TIA

Originally Posted by RR

Since it was never done no calculators were ever designed for it.

Maybe not used often but they had 'em!

http://maritime.org/doc/attackfinder/replica/iswas-sample.jpg The Germans had a similar one (image enlarges...from my 'Ma deuce' thread post #12) EDIT: Submarine Attack Course Finder Mark I Model 3, O.D. 453, 1922. This describes the circular slide rule commonly know as an “is-was” used to calculate an approach and attack by an submarine.
Torpedo Angle Solver Mark VIII Operating Instructions, O.D. 3518, 1941. This describes the hand operated torpedo angle solver commonly called a “banjo”. It is used to calculate the gyro angle when the Torpedo Data Computer is not available

[Raven Morpheus]

OK thanks guys, I think I'll stick to using my calculator for now though, just wondered what was used "back in the day".

[Rockin Robbins]

Originally Posted by Aktungbby

Maybe not used often but they had 'em!

http://maritime.org/doc/attackfinder/replica/iswas-sample.jpg The Germans had a similar one (image enlarges...from my 'Ma deuce' thread post #12) EDIT: Submarine Attack Course Finder Mark I Model 3, O.D. 453, 1922. This describes the circular slide rule commonly know as an “is-was” used to calculate an approach and attack by an submarine.
Torpedo Angle Solver Mark VIII Operating Instructions, O.D. 3518, 1941. This describes the hand operated torpedo angle solver commonly called a “banjo”. It is used to calculate the gyro angle when the Torpedo Data Computer is not available

The banjo, or its Axis equivalent, was NEVER (that's "not often" divided by zero) used by any submarine during World War II by any navy, either Allied or Axis to calculate speed based on target length. It also was not intended to be used for such a purpose. Real submariners would have laughed at you for proposing such a preposterous idea.

By the way, the banjo was used by most tracking parties on American fleet boats. One guy had the banjo, running the same problem that was in the TDC. If they didn't agree the sub didn't shoot. They started the targeting process all over. So it was used A LOT!

But never to calculate speed based on target length by the wire. That calculation is entirely useless. If you calculate 8 knots as the speed using it, that actually means "some random speed between 4 and 16 knots." It's an entirely useless piece of information unless it's an excuse for laughing at it.

[aanker]

Kim Ronhof designed one and it can still be downloaded, printed & the pieces cut out and assembled.

This picture below is from a PTC friend who volunteered at the museum and submarine in Wisconsin:
http://www.wisconsinmaritime.org/the...nce/uss-cobia/



Happy Hunting!

[Rockin Robbins]

That's a bearing rate computer not used for deriving target speed based on target length. It must be used along with the bearing rate charts not even part of Silent Hunter 4.

Basically it estimates speed based on the change of bearing change per unit time. Just as a thought experiment, you can understand that a target moving at right angles to your viewing angle (AoB 90º), the further away from you it is, the slower the bearing changes.

Now visualize an attack where you are at 90º from the target track but it is approaching from five miles away. At first the rate of bearing rate will be agonizingly slow, perhaps a degree in several minutes. But as it gets to a bearing of 350 or 10, depending on which direction it is coming from it will change one degree in a second or very few seconds.

From the Submarine Torpedo Fire Control Manual:



It was a very fussy and error prone procedure with lots of provisos in there which would warn the sensible to avoid such a procedure!

Here's how you plot your data on the maneuvering board that Silent Hunter somehow totally left out of the game:


And here's the bearing rate data form that also got left out of the Silent Hunter series:


Regardless of what you understand or do not understand as a result of this tour of reality, none of this has any relationship to calculating target speed by timing the length by the wire. Maybe we could talk about using a Ouija board?

[Aktungbby]

GADZOOKS! My mistake!I do recall reading, decades ago?, an account of WW II submarining involving use of the is-was but did not grasp it's backup to the TDC function.(Run Silent Run DEEP?) I completely overlooked the op's target length issue... http://www.subsim.com/radioroom/showthread.php?p=434901#post434901 http://www.gizmology.net/sliderules_mancomp.htm

[Rockin Robbins]

Originally Posted by Aktungbby

GADZOOKS! My mistake!I do recall reading, decades ago?, an account of WW II submarining involving use of the is-was but did not grasp it's backup to the TDC function.(Run Silent Run DEEP?) I completely overlooked the op's target length issue... http://www.subsim.com/radioroom/showthread.php?p=434901#post434901 http://www.gizmology.net/sliderules_mancomp.htm

Got enough doo-dads on that there periscope? I wanna hang my rabbit's foot on there.

Oh, yeah, you hit it right on the head. Ed Beach explained the use of the is-was in combat with the TDC in Dust on the Sea, the second book of his Run Silent Run Deep trilogy. What great books for learning how to run a boat! They go way beyond fiction to be required reading for World War II sub enthusiasts. They teach you to think like a sub commander.

[aanker]

Originally Posted by Rockin Robbins

That's a bearing rate computer not used for deriving target speed based on target length. It must be used along with the bearing rate charts not even part of Silent Hunter 4.

I thought it would be of interest, I know what it is and does, and even made one out of sheets of Acrylic with a string.

CapnScurvy has a very nice pic of a 'slide-rule' (Omnimeter) from USS COD j.... there are many do it yourself patterns for it but his pic is the real deal:

From CapnScurvy's Optical Targeting Correction:
http://www.subsim.com/radioroom/showthread.php?t=181172

This is an image of an original Omnimeter made by and for the USS COD.....

The most advanced TDC (as you said), and the primitive tools developed to sink shipping.
Plot, plot, plot and plot.

[Aktungbby]

Originally Posted by Rockin Robbins

Got enough doo-dads on that there periscope? I wanna hang my rabbit's foot on there.

Oh, yeah, you hit it right on the head. Ed Beach explained the use of the is-was in combat with the TDC in Dust on the Sea, the second book of his Run Silent Run Deep trilogy. What great books for learning how to run a boat! They go way beyond fiction to be required reading for World War II sub enthusiasts. They teach you to think like a sub commander.

Originally Posted by me

2 Onkel Neal in his truck thread: Welcome to the true conning tower of the open road; no one gets born with a shifter in hand, so ask away!

Originally Posted by OnkelNeal

Haha, true conning tower, indeed. I feel like a U-bootman,living in this tiny space. I have to move my TV tray/laptop desk every time I want to go forward. It's really cool, I'm digging it.

Think like sub commander?!: driving eighteen wheelers in white-out blizzards, 30ft viz max and U can't pull over/off 'cause nuthin's plowed, in Iowa on I-80 or crossing the Manhattan bridge (with NYC's precious strawberries) into lower Manhattan whilst monitoring your CB and the early primitive radar detectors (sneaky bears: covered X and K band only...practically the 'metox' of its day!)...from the 'conning tower of your Freightliner-all the while formulating your avatar ....35 years in advance.Monitorin' your airbrake pressure, brake pad's temps, and numerous diesel related dials on the 'dives down' or 'ascents up' Donner: 7000 ft over 30 miles for example, makes SH child's play. Computing eight lbs. a gallon fuel x four miles a gallon by the time you cross a state port-of-entry scale to make legal axel-weight----where's my fuel is-was? Where's the goddam Captain of this rig anyhow??!!...Oh crap...it's I ....

[Rockin Robbins]

All the cool stuff that never got into the game! And don't even get me started on missing sonar goodies!

People think that Silent Hunter is the last word in WWII sub simulation! I'd argue that it hasn't even reached first word status in many aspects.

That is reflected by the fact that gamers think that calculating speed by timing ship length by the wire even makes sense. It makes sense to us because we have perfect information. Real subs didn't and would never consider such an abomination.

[BigWalleye]

Just an aside: Both Fluckey and O'Kane mention IDing a target as much as 24 hours after it was successfully attacked. So you can figure that a correct target ID was not considered critical to the fire control solution. Hitman, over on the SH3 forum, has researched the optics of existing WW2 U-boat periscopes, and most after 1940 apparently did not even have a stadimeter. It seems that this device was removed to allow room for a binocular eyepiece. KM doctrine called for ranging using the scope graticle, a rechnique which in the sim is fast and reliable enough using rough rule-of-thumb mast and funnel heights. For this technique, no positive target ID is required. SH4, AFAIK, does not allow manual entry of target mast height, as was done historically. (They didn't have an interactive Identification Manual!) Without a manual mast-height entry capability, there is no way to use the American stadimeter except by IDing the target. (If this statement is wrong, I hope someone will post the correct technique. It would be extremely useful.)

[Aktungbby]

Originally Posted by edwauarallen

Have been watching episodes of silent service and it seems to me that
they used the surface radar a lot. Isn't this a bit reckless because of
the risk of detection.

Originally Posted by BigWalleye

Just an aside:I hope someone will post the correct technique. It would be extremely useful.)

^An aside of your aside Sir! As of tHis AM: some new insight in this mind-boggler article I found for Edwardallen's inquiry as to use of radar both submerged and/or surfaced at night...apparently operating radar wasn't lethal as all-get-out for US subs vs Jap radar-detection. Submerged radar compelled sluggish battery power but was still utilized. No need for a stadimeter with the radar? read carefully it's not easy going: Pg. 31 in particular and the use of SJ surface radar: http://www.cnrs-scrn.org/northern_mariner/vol14/tnm_14_3_27-40.pdf In short, end run tactics, great escort threat awareness, getting ahead of convoys from 18,000 yards with partial submerged (still using radar) tactics all figured in 1943 to horrifically boost tonnage in the Pacific war. pg. 37; Radar completely changed the relatively poor night-vision Mahan prewar stealth/scout tactics; provided security against escorts; accounted for targets otherwise missed, and made post-attack escape planning a real possibility. The US sub, with radar tactics could aggressively surface attack with impunity on her terms. pg.40