Naval History Forums

Thanks my friend, I have read some parts from the Eugene Slover web. But I think that it lacks some details.

tommy303 wrote:My understanding is the 1* figure may be an average theoretical error, although in a properly functioning gyrocompass the actual error is 0.0 to 0.5*. Power failure to the gyro compass can completely throw off the accuracy, even after being restored, thus requiring recalibration of the master gyro compass. In the Kriegsmarine this was the job of the Navigation officer who would use an azimuth circle or parallel motion protractor fitted to an above deck gyro compass repeater. These would measure the azimuth of the sun indexed against true north and the results checked against the compass card. The card would then be adjusted to true north, and all other repeaters and the master gyro compass would be adjusted to suit. The regulations required the gyro compass be checked for errors daily, but usually, unless there had been a major failure in the power system, little or no recalibration was necessary, which was just as well as bad weather would make it difficult or impossible to measure solar azimuth.

As the fire control system was dependent on the master gyro compass for directional reference, it's accuracy was only as good as the calibration of the gyro itself. ..........

Just to add some to Thomas's comments, Once it became clear in 1935 that the GEMA radar could become an operational reality, the KM also contracted GEMA to help improve the reliability and accuracy of the gyro systems:

"A special device was the difference -gyro-compass 'daughter' which showed deviations between gyros, and which was duplicated on warships....when the deviations exceeded a given amount it triggered an alarm that indicated one or more gryos were not in order." (von Kroge)

GEMA was involved with a lot more than radar and sonar. They designed and built all kinds of specialists electronics for warships ranging from relatively secure TBS communications to electronic measurement, transmissions, and switching systems, as well as electronic navigation and ship control systems. Many of these assets were absorbed in West Germany by Siemens after the war, as by 1944 GEMA and Siemens were very closely associated.

Marcelo has touched upon an over looked aspec; that the radar accuracy could be thrown off by the mechanical apperatus the radar antenna was mounted to.

Most here are aware that the optics on German large warships did not use a combined "director" apperatus to mount and traverse both the rangefinding and the directional finding instruments (nor the night/low visability optical systems). This had important implications to the developmental course of radar in the KM.

Since the optical rangefinder mountings originally did not need to attain a fine degree of precision in bearing measurement, they were not ideal for measuring radar derived bearing data, but they were the most practical place to mount the required relatively large antenna. Additionally, the large rangefinder assemblies aloft were already fully stablized. This was nonetheless, a factor in the early rejection of lobe switching aboard ship by the KM. To incorporate lobing on the big ships, modifications and revisions had to be made to the rotating rangefinder mounting assemblies; their mechanicals, their electrical motor drives, and their alignment systems. Accuracy could then be measured in fractions of a degree.

These modifications were subcontracted wholely to AEG (Allgemeine Elektrizitaets-Gesellschaft). AEG was a well established defense contractor in Germany.

marcelo_malara wrote:Thanks Brad for your long explanation.

So I understand that the radar only changed the instrument used to measure the range and bearing, the plot still being necesary to determine range rate. Am I right?

Basically yes, but it’s a bit of misnomer to say that radar determined the bearing. Fire control radar was always fixed to the director thus allowing the director to track the target in bearing in blind fire conditions. Early radar installations still required plotting to determine range rate, later installations didn’t require this but it was done as a back up. The technique with later installations was for the operator to change the course and speed of the target setting until the present range indicator on the rangekeeper was matched up in value and rate with radar range indicator. Plotting was still done to assist the rangekeeper operator but there is a natural latency in this data. The main point is that the rangekeeper operator didn’t have to wait for range rates form the plotter operator.

-Bearing was plotted too?

Not in the American system, sight deflection was, which is basically the total lead the guns are required to hit the target at its future position at the time of impact.

-Teoretically you can derive target course and speed (and from them range rate and deflection, and from deflection and range bearing rate) from a series of target´s bearings and ranges. Was in WWII any computer (or rangekeeper) capable of solving this

Yes, the American Mark 1A computer for the secondary battery was able to do this for aerial targets (oddly not for surface targets) and the British AFCT Mk X was able to do this.

Brad Fischer

I want to thank Brad for his very valuable contribution here.

I also do!!!!

Brad Fischer wrote:..........
Now radar didn’t change things overnight. Initially it was in effect a more accurate all weather rangefinder........
Thus even under ideal ranging conditions and with highly experienced operators optical ranging is at a disadvantage to radar in terms of accuracy (as well as the afore mentioned latency)..............
..........In the end, optics were hard pressed to keep up with the range aspect of fire control problem. They did have advantages particularly in survivability and durability. They also were superior in bearing tracking and deflection spotting. Thus a combination of optical bearing track and spot with radar ranging and range spotting was considered the ideal setup..........

Now that I have some more time I would just like to write that I am in agreement with Brad's comments.

The relatively accurate and the relatively quick measurement of distance, is the single most important function of a radar system. Moreover, radars' strongest function just happens to be the weakest function of purely optical systems.

The accurate and relatively quick measuerment of range, and resolving the spatial relationship for distance between multiple objects, is the weak link of optical systems. Optical range finding compares poorly to electronic range measurement. Howse compared the range accuracy of Type 284M to the rangefinders aloft on the KGV class battleships. The 284's range accuracy was nominally +/-150 yards, while the rangefinders aloft had a typical range accuracy of +/- 1,000 yards.

Even a relatively simple range taking radar, while not as capable overall as more sophisticated systems, still provides the primary function, and can make for a large difference in capability compared to not having radar.

tommy303 wrote:
My understanding is the 1* figure may be an average theoretical error, although in a properly functioning gyrocompass the actual error is 0.0 to 0.5*.

Seems 0.0-0.5* more suitable for modern devices because it is extremely small actual error in case of the ship yaw. I note that the gyrocompass error at least three times as much when ship heeled or turned. This affected fire control solution in principle. Our battleship Marat on 1941 had 3 girocompasses, two "Kurs-2" and one "GU mark 1" with such specification:
Kurs-1 or 2 (date in service 1937, a soviet copy and second modified model of "New Anschutz" girocompass. I not sure that "New Anschutz" a proper model name, as said, this original model was designed in 1926 in Germany)
accuracy, degrees:
steady course +/-0.3-0.5
changing course +/-1.0-3.0, for mod.2 +/-1.0-2.0
rolling and pitching +/-1.0-2.0
GU mark 1 (date in service 1931, a soviet copy of old Sperry gyrocompass MkVIII)
accuracy, degrees:
steady course +/-0.5-1.0
changing course +/-2.0-4.0
rolling and pitching +/-2.0-3.0

Also, I under impression that you refered to Anschutz girocompasses. But it is top device due to excelent characteristics. In the middle of thirties was appointed a commission of soviet experts which tested Sperry vs Anschutz gyrocompasses. Up to this date the Red fleet traditionally purchased only Sperry devices. As a result all Sperry devices was finded unreliable and difficult in operating. So, Anschutz was a choice as prototype for manufacture Kurs-1.

Regerds,
Sergei

Although the original post was more in the context of ship to ship radar fire control, I find the problem of shipboard radar direction of Flak far more interesting. It was certainly a far more complex and difficult problem.

Above we have examined some of the elementary and early solutions to problem of shipboard flak direction by radar, but these early systems such as the MK4 (FD) and the Type 285 were very much entry level radars systems for Flak control. Although certainly better than no radar at all, they were never as effective in reality as many people today believe.

To make the step to the next level of effectiveness, conical scanning radar with auto tracking and lock on was required. The Allies were aware of the Wuerzburg innovations in this regard, having first captured a Wuerzburg C in Feb, 1941, and by mid war, more advanced versions of Wuerzburg had been captured in the Med. Nonetheless, it wasn’t just a simple matter of mounting a Wuerzburg or SCR584 aboard ship. They were several technical problems that needed to be solved to make conical scanning feasible aboard ship.

Conical scanning using a dish type of radar antenna produces a pencil shaped beam and that requires the antenna to have a fully stabilized mounting. Furthermore, with such a beam it can be very difficult for the radar to blindly aquire the target, and with auto lock on and tracking, the radar might lock onto a phantom target when operating over water.

Spectral reflection, or the reflections of the target echoes off the surface of the water can be a special problem of any radar ranging of aircraft low over the water. A sure sign that the radar is erroneously ranging on the reflective echo, instead of the actual target aircraft, is consistently shooting short of the target, as if it’s over estimating the speed of the target. Conical scanning radars are especially vulnerable to spectral refection problems, because it is so difficult to determine the reflective echo from the target echo. A master radar to put the conical scan radar onto the target might be needed in some cases.

Solving these problems took time and the problem of spectral reflection proved most vexing to the team that was trying to develop a blind landing system for aircraft from the SCR584, and trying to develop naval versions of SCR584 for Flak direction aboard ship. This was in part the reason the German development of Euklid, and the eventually mounting of a navalized Wuerzburg D aboard warships, was so protracted. The British Type 275 was also very protracted, probably for the same reasons.

Type 275 used two 90cm dish antennas. One was for send and the other for receive. Only the receiving dish had a conical scan. It wasn’t until very late 1944 that Type 275 began the initial set of sea trials. Therefore, Type 275 would not become an operational reality before the end of the war, and was on about the same schedule as the German Euklid that would have became operational with fleet units by April 1945. The British were also developing a 3cm gun laying system for light Flak called Type 262. The 262 would be mounted right on the 40mm Flak guns called the STAAG (stabilized tachometric anti aircraft gun). The STAGG and it’s radar control system would not become operation until well after WWII.

The USN was following far behind the British and the Germans with the MK35. It wasn’t until the 1950’s that the basic FD system (with the Mk12 and Mk22 upgrades) was finally put out to pasture. Indeed as late as the Korean War, major USN warships were still without Mk35. It wasn’t the development of Mk35 itself per se, but the huge problem of refitting so many warships with the new equipment, and especially a better director system, that was the hold up.

However, really effective radar direction of Flak aboard ship was a post WWII reality in most cases.

Dave,

If it was that bad, why do we have reports of first round hits with 5"/38 VT rounds at long range? It would seem impossible according to your description. The FC system would have had to get the round within a few feet of the target for the fuze to be activated, right?

In fact, from reading your post one would get the impression that the Kamikazes should have been able to sink every ship in the US fleet, when in actuality quite a few of them were shot down by AAA. Far more than zero, I would say. Your post would leave me the impression that it didn't work at all.

I respect your research. You have found out a lot of valuable information. However, I do wonder whether you have taken reports of problems with these systems to mean that they didn't work at all. In the case of US ships, I know that if they weren't able to shoot down one plane and that plane hit a ship, the ensuing report would make it sound like a worthless system and the writer may well have felt that way at the time.

Dave Saxton wrote: ....... Although certainly better than no radar at all, they were never as effective in reality as many people today believe. ........However, really effective radar direction of Flak aboard ship was a post WWII reality in most cases.

To quote myself, I think I'm making it clear that the performance was relative, and relative to what could be accomplished with more advanced systems, it was not not as good as most people think. It was not "worthless", far from it, but not the revolutionary improvement often ascribed to it. Radar had yet to come into it's own in this particular arena. Furthermore, the greater number of aircraft destroyed by USN shipboard AA during the war, were destroyed by the light flak weapons after the aircraft had already got in close, or as they overflew the ship. These ligher automatic weapons usually did not have any radar control at all. However, the American light Flak did have the advantage of an exceptional optical sight designed by Dr Stark Draper of MIT. The Draper sight did provide a remarkable improvement in the effectiveness of USN light Flak. To really take advantage of the V/T fuze however, a more advanced, and more accurate, radar generation was needed.

A longer range targeting of a higher flying aircraft is actually a much easier problem for radar like the Mk4 than a close in targeting of a low flying aircraft.

Dave Saxton wrote:

Dave Saxton wrote: ....... Although certainly better than no radar at all, they were never as effective in reality as many people today believe. ........However, really effective radar direction of Flak aboard ship was a post WWII reality in most cases.

To quote myself, I think I'm making it clear that the performance was relative, and relative to what could be accomplished with more advanced systems, it was not not as good as most people think. It was not "worthless", far from it, but not the revolutionary improvement often ascribed to it. Radar had yet to come into it's own in this particular arena. Furthermore, the greater number of aircraft destroyed by USN shipboard AA during the war, were destroyed by the light flak weapons after the aircraft had already got in close, or as they overflew the ship. These ligher automatic weapons usually did not have any radar control at all. However, the American light Flak did have the advantage of an exceptional optical sight designed by Dr Stark Draper of MIT. The Draper sight did provide a remarkable improvement in the effectiveness of USN light Flak. To really take advantage of the V/T fuze however, a more advanced, and more accurate, radar generation was needed.

A longer range targeting of a higher flying aircraft is actually a much easier problem for radar like the Mk4 than a close in targeting of a low flying aircraft.

What weapon was the Draper sight used on? I'm thinking 20mm, which was considered all but useless against Kamikazes. How about the Mk51, which was the director for the 40mm bofors? It used rate of train to provide lead to the operator. Also, is it possible your statistics related to light flak being more effective are for the entire air war in the Pacific and not the period in late 1945 when the Kamikaze was such a big problem?

I believe that conventional wisdom was that you needed to seriously damage an attacking Kamikaze before it got within effective 40mm range in order to have a good chance to stop it before it hit your ship. If it got closer than that, a direct hit from a 5" shell would be needed to stop it unless you got a lucky hit. That is why the USN had all but discarded the 20mm and even 40mm in ships built near the end of the war.

Of course, other things could happen to the Kamikaze. It could be shot down by fighters, and many were. It could be damaged or shot down by escorts, and some of that was probably high altitude hits from 5" guns as it passed over. I'm sure some of it was also 20mm and 40mm fire as it passed one or more escorts, but it would have to be pretty close for that.

All in all, I suppose I don't have a problem with your overall assessment. It's just that the weapons and radar that existed were able to muddle on, and the 5" in particular had to be relied on because Kamikazes were so hard to stop once they got within 40mm range. 40mm was IMO more of a point defense weapon where 5" could hit things trying to get between escorts. One thing about crossing targets is the range rate isn't as high, but you have to be able to train your gun fast enough to hit one. You sometimes also hit your own ships, and that did happen from time to time.

Right I'm looking at this as the overall problem of radar directed firecontrol of Flak, and not specifically narrowing it down to the late war Kamikaze problem.

It would appear that the Draper sight was the one used for the 40's, and is probably the same thing your refering to, the "Mk51" possibly being the associated director for the Draper system:

" Not only was the 40 a better gun for close defense, it had the excellent Mk14 optical commputing sight (Draper sight) ...."(Brown)

And elsewhere when adressing the problems of the overall Mk4 type radar firecontrol system not coping well with the Kamikaze attacks Brown writes:

" Once the Kamikaze were within their range, the non radar 40 and 20mm guns had to save the ship and often did."

I won't take up the space to quote Brown more fully here again, but I'll point out that he's not saying that the 5" with the V/T fuse wasn't effective, but that it wasn't effective enough, or as effective as it could have been. It was certainly destroying a % of Kamikaze attackers, but at the same time it was still letting far too many through.

I agree that the light automatic Flak wasn't up to the task of stopping Kamikaze attacks. The stopping power wasn't there. IIRC, the USN was investigating going to an homogenous 3" light flak battery, as the war came to close. The Army used an excellent 90mm gun. The Vanguard despensed with the 20mm altogether and had an homogenous 40mm light flak battery. On the other hand modern 20mm flak are still in use today, but they have much higher ROF than the 20mm Orlikon's did. With a high ROF a 20mm could still be very effective at anti-aircraft. Russian designed, IIRC, 50mm and 38mm light Flak, proved deadly enough in Vietnam, but they were essentially directed by reverse engineered copies of the 584 too.

"

I agree that a 40mm radar directed gun can be very effective today. Actually, the rate of fire of the WWII water cooled bofors was 140-160 rds/min/gun when horizontal and 120 at high elevation, so pretty fast. Modern jets can avoid them by flying higher than they can fire effectively, but then of course they have to deal with missiles.

The DesMoines class CAs were commissioned with a 3" AA battery, replacing a quad 40 with a twin 3". That weapon was used until replaced by missile armament and CWIS.

I have become quite interested in radar assisted AA FC as well. This site has a lot of valuable info, including some really interesting bibliographical data:

http://www.rnmuseumradarandcommunicatio ... E%2019.htm

and this page:

http://www.rnmuseumradarandcommunicatio ... 20PAGE.htm

This document in particular contains a list of every publication/document of pertinence to radar and radar FC, in the RN during WW2:
It is found on this page: http://www.rnmuseumradarandcommunicatio ... 0STORY.htm
of the RN Radar Museum website.



Lately, I've been quite interested in the ABU and Continuous Prediction Unit (CPU) which the RN used for AA FC for nominally non DP weapons such as 6", 8" and probably even 14, 15 and 16" guns, and for blind fire and barrage fire of DP weapons. I am also very interested in the evolution of HACS III and IV through GRU/GRUB and Type 285/282 radar upgrades.

I also discovered that the IWM has a copy of a WW2 RN ABU training film, and for a fee will copy it to VHS...