Naval History Forums

Hi everyone!

I have been wondering which methods the crew had to calculate the speed of the target? Did they even bother to measure target speed precisly when they were steaming at 30 knots themselfs?
I assume they first needed to guess the distance to the target and then look at variables like target heading, degrees travelled over time and subtract own travelled distance.
Did they really do that before opening fire at Hood, or was distance and target heading enough to start firing?

Kind regards,
Daniel

It's very complicated when getting into detail. In very simple terms, distance and target bearing really only work if both targets are stationary. In order to correct for projectile time of flight, one has to know one's own speed and course, target speed and course. plus current range and bearing, thereafter using all of this data to predict (or one might more properly say, estimate) target range and bearing one time-of-flight into the future. One COULD, of course open fire with only range and bearing -- i.e. there is nothing in the laws of physics preventing it, but unless the range is very short, your chances of hitting are very small.

Bill Jurens

Good day Bill!
Thank you for your answer.
Regarding own ships speed and course, would Bismarcks target computers automatically update the info from the "speedometer" and gyroscope? If hand cranked it would still be fairly easy data to collect.
Range to target would be collected from the different stereoscopic rangefinders or the radar and fed into the computer, wouldn't these be fairly accurate even though Bismarck and/or the target was moving?
Targets bearing I imagine requires a few dots on the map made by distance readings with a certain amount of time in between. Would this be how you calculate speed of the target aswell?
I never saw a photo of a german fire control computer, so I wonder which inputs it would take.

Kind regards,
Daniel

from earlier posts
accuracy of optical measuring against target ship
black line true distance
dotted black line average from all measuring units
coloured lines individual measuring units.

using funkmess improves accuracy to about +-50 m for "Entfernung fein" for Fumo 26/27
even under bad visibility conditions (rain fog night).

But at bad visibility conditions identifying friend or foe appears as the main problem especially in melee situations.




-----------------------------------------------------
theoretical performance of a 10m RuM, distance data are submitted automatically into the fire control equipment for distances in between 3 km to 45 km


the "Mindestfehler" -Minimum error is caused by the eyes ability to resolve adjacent objects.

Thanks Thorsten!
This is very interesting data for my simulation.
Do you know what xx-Facher means?

If I understand correctly the atleast one of the ships are moving according to the first document, any info on how fast they were steaming?

Kind regards,
Daniel

Hello Bracer,

Initially, a pure eyeball estimate as per

To commence tracking it is only necessary to introduce estimated values of target speed and target course (or target angle), and energize the time motor.

from OpanaPointer's excellent reference. My underlining.

Once the computed azimuth starts to wander compared what you are seeing it might indicate estimated speed is wrong (since yours should be about right) and should be adjusted up or down. Much harder is estimated enemy course. Easy to be ten or more degrees out. If the enemy is kind enough to head straight towards you or away ie inclination 180 degrees or zero degrees you can get his course easily, and range change will give you his speed. (German inclination system might be the reverse of British) Hmm, I wonder if Admiral Tovey, the "head-on attack" enthusiast considered this situation?

Nice reference from Thorsten too. Wonder how they knew black line "true" distance? Were both ships running on surveyed-in railway lines for instance?

Another great reference is the Royal Navy version- The Pocket Gunnery Book, more introduction than hands-on manual.https://maritime.org/doc/br224/part3.htm

All the best

wadinga

Thank you for the links!
They are indeed interesting.

I find no reference to a computer/tool which would help estimate targets speed or heading.
So I assume it was done with pen, paper and a ruler, based on range and bearing of the target at different times.

Kind regards,
Daniel

bracer wrote: ↑Sun Mar 10, 2019 5:38 pm Thank you for the links!
They are indeed interesting.

I find no reference to a computer/tool which would help estimate targets speed or heading.
So I assume it was done with pen, paper and a ruler, based on range and bearing of the target at different times.

Kind regards,
Daniel

Here's the manual for the Admiralty Fire Control Clock - a reduced version of the AFCT:

https://maritime.org/doc/afcc/index.htm

Basically, the director GCO will enter a range, bearing and estimated course and speed for the target. The director team then keeps their sights on the target, and sends corrections to the AFCC/AFCT if the director cross-hairs drifts off the target and if the salvo lands over, short or left/right of the target. Using the inputted corrections the AFCC/AFCT will converge on the correct solution as only one combination of range bearing, speed and course will keep the target in the director crosshairs.

bracer wrote: ↑Sun Mar 10, 2019 5:38 pm Thank you for the links!
They are indeed interesting.

I find no reference to a computer/tool which would help estimate targets speed or heading.
So I assume it was done with pen, paper and a ruler, based on range and bearing of the target at different times.

Kind regards,
Daniel

IIRC the IOWAs had analog computers, they were operated by the ship's band.

bracer wrote: ↑Fri Mar 08, 2019 1:35 pm
Do you know what xx-Facher means?

If I understand correctly the atleast one of the ships are moving according to the first document, any info on how fast they were steaming?

Kind regards,
Daniel

xx-facher
the 10 m RuM's(rangefinders) had 18 - 50 fold magnification

only two ships
Admiral Graf Spee(measurer) vs Admiral Scheer(target)
the different coloured lines are the individual measurings of every single 10 m RuM (main fc-control station, after fc-control station, turret A, turret B
(Addition since summer 1939 Admiral Graf Spee had a fc-radar ranging unit) as the first ship in warservice.


speed was in the order of ~20 sm/h

wadinga wrote: ↑Fri Mar 08, 2019 8:00 pm
Nice reference from Thorsten too. Wonder how they knew black line "true" distance? Were both ships running on surveyed-in railway lines for instance?

both ships were observed by shore "Langbasisgeräte". Accuracy of the Langbasisgeräte was significantly better then the usual range measuring devices mounted on ships, as the "lenght of the Basis" was in the order of 50 m.

Hello Thorsten,

So given the accurate azimuth of the fixed baseline, plus two highly accurate measurements of azimuth from the ends, the remote positions of the ships were derived. Interesting.

All the best

wadinga

wadinga wrote: ↑Mon Mar 11, 2019 12:53 pm Hello Thorsten,

So given the accurate azimuth of the fixed baseline, plus two highly accurate measurements of azimuth from the ends, the remote positions of the ships were derived. Interesting.

All the best

wadinga

The sort of "range-finder" Thorsten describes was common in modern coastal defense systems. The "two highly accurate measurements of azimuth from the ends" equate to "adjustable prisms" used in a ship-borne optical rangefinder ..... except that the base-length might be several hundred yards rather than some tens of feet. The rest is a trigonometry problem.

B

I broke my math bone in the fifth grade and it never healed right. Math will never save my life.