Fire Control + Radar Questions

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Garyt
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Fire Control + Radar Questions

Postby Garyt » Wed Jan 14, 2015 8:47 pm

Had a few questions on fire control. I'll give a bit of my understanding how they work (which may well have some inaccuracies), and then a couple of questions.

I'd appreciate any help on the questions, and feel free to correct any inaccuracies :D

My understanding is they function roughly as thus:

Information is input into the fire control computer. Things like target range, bearing, and speed. I'd think the shooters bearing and speed would need to be input as well? Then the solution is calculated, after rounds are fired fire is corrected based upon the fall of shot. I've even heard things like wind speed are included.

Questions:
1) Radar is used for range in some of the systems. I've heard Japanese systems are more where radar helps a little, while the later war more advanced US systems are truly radar assisted. Why is this? Is the Japanese radar less precise (Think I have read this based upon band width)? Do the US systems integrate radar better?
2) Is radar used for target speed or bearing, even on the more advanced systems?
3) I've heard some radar is able to observe something as small as fall of shot, other radars are not able to?
4) How much type is spent on input and computation prior to a firing solution being determined? I know there are a lot of factors, including what system being used, but looking for some rough ideas.
5) I've heard optical rangefinders are about as effective as determining range - which would make an optical based system similar function similar to one with a radar range finder I would think if visibility is good? Though bad visibility does not have to be night. Could be a squall, hazy, anything other than optimum visual conditions.
6) Blindfire - what makes fire control capable of blind fire? Is the radar giving range, bearing and speed of target? How accurate was blindfire in actual engagements if anyone has specifics. And I would think blindfire as truly that- no using gunflashes, illumination rounds, etc. etc.

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tommy303
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Re: Fire Control + Radar Questions

Postby tommy303 » Thu Jan 15, 2015 1:00 am

Firing solution is based on target bearing, course, speed and range, own ship course and speed, wind direction and velocity, barometric pressure, and ballistic properties of the guns in the battery and ammunition type being used.

As to your points:
1. Radar was and is most valuable in range to target determination. Early on range errors were quite small though bearing errors were imprecise enough for doctrines to hold to using optical bearing determination rather than radar bearing. One might call the early fire control radar systems radar assisted rather than radar controlled. As systems got better and more integrated into the fire control system, radar became increasingly important to such an extent that the roles of radar versus optical were reversed with optical becoming an assist to radar rather than the other way around.

2. Radar is currently used for range and bearing data. The radar plot, can help in estimates of enemy course and speed based on rate of change in bearing and range.

3. Spotting fall of shot is certainly possible with radar, though the actual maximum range at which fall of shot can be observed differs widely between various radars.

4. Once all the data on needed to produce a reliable rate of change from the fire control computer has been fed into the range keeper (AFCT, Schusswertrechner, etc), the fire control system will begin producing a continuous string of solutions which can be further modified by applying corrections based on fall of shot or observed errors in target bearing and range prior to opening fire. The corrections do not entail starting over again, and are applied as the system runs. How long is spent depends on the situation. If the enemy is clearly visible at extreme range, the fire control team might take their time double checking enemy bearing and range against the rate of change solution and apply corrections as needed. If on the other hand, the enemy suddenly appears out of a fog bank, only a couple of minutes are really needed for a rough solution to be calculated and fire opened; there after correction would be based on fall of shot.

5 In range determination, radar is usually much superior to optical range taking. Optical bearing information was more accurate though compared to the early radars.

6. To have an effective blind fire capability, one has to have a fully integrated system with reliable range and bearing capable radars. Accuracy would depend largely on the ability of the radar operator and the scale he was using. German shore batteries demonstrated quite early in the war a reliable blind fire capability against convoys moving up the English Channel.

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Re: Fire Control + Radar Questions

Postby Thorsten Wahl » Thu Jan 15, 2015 11:48 am

additionally inputs as water had no solid surface
the firing solution must be continuously corrected for movements of the own ship around (pitch, heel, yaw) and along A, B and C axes
(ie corrections for trunnion tilt)
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Re: Fire Control + Radar Questions

Postby Dave Saxton » Thu Jan 15, 2015 3:17 pm

The most important function of radar in firecontrol was and is the measurement of range to target. Here radar has the advantage over optics if there is any impairment of visibilty at all.

In terms of range measurement for firecontrol, a "primitive" radar is just about as helpful as a "highly advanced" radar. The range accuracy of a primitive set will probably be just about as accurate as a highly advanced system and it will probably be more accurate than optics under most conditions. Usually it will be within 100 meters, which is within the typical dispersion tolerances for naval guns. For example, the USN found that their radar range accuracy was 0.1% of the range to target plus a tolerance. On the other hand the range accuracy of the large USN optics was typically about 1% of the range, or less accurate by a factor of ten. Therefore, the accuracy of the optics at a target range of 25,000 yards was would typically be 250 yards, while the range accuracy of the early Mk3 radar would be 65 yards (0.1% x 25,000 + 40 yards) at that range.

This was not the case with the early German radar, not because the radar wasn't accurate but because of the astonishing accuracy of the large German optics. Thorsten has posted the test results of pre-war trials of these optics on the panzershiffs. It was typically within 30 meters at ranges up to 23km. The early Seetakt had a range accuracy and a resolution for range of 100 meters. Therefore, radar became considered secondary and optics primary unless the visibility impaired the use of optics. This thinking was difficult to over come in the minds of commanders even after the radar accuracy improved to be better than the German optics.

As Tommy wrote, radar range taking became primary for firecontrol through out the world during WW2, but blind fire in the case of surface gunnery (for air targets the bearing accuracy for elevation must match that of side to side) also requires a bearing accuracy of at least 0.2*. Such bearing accuracy wasn't consistently obtained from ship board radar during WWII. Radar with lobe switching or beam switching, or some form of beam scanning, could obtain such refined bearing accuracy but not always consistently, due to slack in the director's traverse drives and tolerances of ship gyro systems. Therefore even late war, the USN recommended that radar range taking be combined with optical bearing measurement -unless the target could not be seen. The Germans and the British followed the same doctrine.

The Japanese did not deploy radar with lobing on their warships before they had no major warships left to deploy it on. However, the Japanese could use their relatively primitive surface search sets to better measure range to target at night or through fog and haze even though it was not a firecontrol set. The range accuracy of 10cm Type 22 (first deployed during 1942) was 100 meters or good enough for firecontrol ranging. They just had to combine it with optical bearing taking.
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Re: Fire Control + Radar Questions

Postby Dave Saxton » Thu Jan 15, 2015 3:52 pm

Tommy mentioned that firecontrol radar be fully integrated for best operation. What this means is that the range and bearing data feed directly into the firecontrol computer system, and that the computer system directly control the aiming of the guns through remote control.

When the Americans first inspected the Prinz Eugen over in Eurpoe after the war they were intrigued to see that the guns automatically aimed at the target the main foretop radar set was aimed at. From 1940 range and bearing of the German radar sets were automatically transmitted to the firecontrol computor via electronic devices rather than being telephoned in and then manually in-putted. This was of course done with optical data since WW1.

When the Artillery Research Command for Ships (AVKS) examined the methods that data was transmitted to the computers on Bismarck they found that it was either or. Either the optical data was transmitted or the radar data was automatically transmitted, but not both at the same time. They ordered modifications of the Siemens equipment so that both could be transmitted automatically at the same time. This was a major step forward toward blind fire. With German radar the range to target was measured constantly by the radar operator keeping the pip centered on the zero point on the fine range indicator. The same for the bearing indication on the bearing indicator. Therefore the firecontrol solution was constantly up -dated second by second in the computers, rather than waiting for the rangefinder operator obtaining a new range measure at intervals.
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Dave Saxton
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Re: Fire Control + Radar Questions

Postby Dave Saxton » Thu Jan 15, 2015 4:26 pm

Splash Spotting:

The ability of radar to spot such things as shell splashes depends on the signal to noise ratio of the radar and reflectivity of the splash of the radar pulse. Another consideration is the size of the discrimination cell (range resolution x bearing resolution).

The USN MK8 radar manual lists the ranges that Mk8 could reliably spot main battery BB caliber (14"-16") shell splashes as 20,000 yards. Mk8Mod3* was Mk8 modified to Mk13 or 3cm operation. The 3cm operation increased the reflectivity of water droplets to the radar pulse and therefore produced a stronger echo signal increasing the reliable range that splashes could be detected. This does not mean that splash spotting is the result of shorter wave length in all cases however.

When KGV's 50cm Type 284 was knocked out by shock by the 12th salvo when bombarding Bismarck, it switched over to the 7.5 meter wave length Type 279 for ranging, and it was found that the long wave radar better tracked shells in flight and picked up splashes better than the 50cm radar did. This was largely because the splash height and the shell's length was a favorable multiple of the long wave length giving a stronger signal.

Signal to noise can also be improved by longer wave length since the noise floor within the electronics will likely be lower at frequencies less than 400mhz. This was why Seetakt changed from 57 cm to 80 cm in 1939. By lowering the noise floor in the receiver, splashes could be better detected to greater ranges. A coastal Seetakt set used splash spotting to correct the fall shot at night, resulting in hitting British convoy ships at 33.6 km range in 1941.

*Mk8Mod2 was adding a repeater Type B indicator in the firecontrol computer room so the computer operators could also see the fall of shot.
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tommy303
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Re: Fire Control + Radar Questions

Postby tommy303 » Thu Jan 15, 2015 5:18 pm

additionally inputs as water had no solid surface
the firing solution must be continuously corrected for movements of the own ship around (pitch, heel, yaw) and along A, B and C axes
(ie corrections for trunnion tilt)


Exactly so. In more advanced systems the correction for pitch and yaw was done automatically by the fire control master gyro or the director sights and incorporated into the range keeper or fire control computer. Rolling movement was generally handled similarly, sometimes with a device that measured the velocity of roll so the guns fired at the optimum point in roll when the firing switch was closed (as in the German Abfeuerunggeraet) or in having a fully stabilized gyro gun sight (RN "P" Sight which not only kept the sights on target but also transmitted correction for pitch, yaw, and roll to the fire control system). In ships without such systems, or in case of break down for those that did, director sights had to be cross leveled manually for pitch and yaw, and the director layer had to use his horizontal wire to hunt the horizon and fire the guns at what he felt was the correct moment in the roll.

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Re: Fire Control + Radar Questions

Postby dunmunro » Thu Jan 15, 2015 6:56 pm

Dave Saxton wrote:

In terms of range measurement for firecontrol, a "primitive" radar is just about as helpful as a "highly advanced" radar. The range accuracy of a primitive set will probably be just about as accurate as a highly advanced system and it will probably be more accurate than optics under most conditions. Usually it will be within 100 meters, which is within the typical dispersion tolerances for naval guns. For example, the USN found that their radar range accuracy was 0.1% of the range to target plus a tolerance. On the other hand the range accuracy of the large USN optics was typically about 1% of the range, or less accurate by a factor of ten. Therefore, the accuracy of the optics at a target range of 25,000 yards was would typically be 250 yards, while the range accuracy of the early Mk3 radar would be 65 yards (0.1% x 25,000 + 40 yards) at that range.

This was not the case with the early German radar, not because the radar wasn't accurate but because of the astonishing accuracy of the large German optics. Thorsten has posted the test results of pre-war trials of these optics on the panzershiffs. It was typically within 30 meters at ranges up to 23km. The early Seetakt had a range accuracy and a resolution for range of 100 meters. Therefore, radar became considered secondary and optics primary unless the visibility impaired the use of optics. This thinking was difficult to over come in the minds of commanders even after the radar accuracy improved to be better than the German optics.



I take reports of 30m optical RF accuracy at 23km with a grain of salt...


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