hans zurbriggen wrote: ↑Thu Nov 02, 2023 3:35 pm
Hi Byron,
thanks a lot, a most interesting document, confirming ranging tolerance of +/-150 yards for Type 284 vs +/- 40 meters of German FuMO radars in 1941.
I wasn't aware that 284 had two panels: "ranging" scope and "warning" scope. I had always thought to 284 as dedicated gunnery radar, therefore only with a "ranging" scope. From what you have posted, it looks like initial range got on Bismarck by KGV on May 27 (25.100 yards) was obtained using less accurate "warning" scope and that 284 operator continued to look for Bismarck using this scope as "ranging" scope max range was 24.000 yards.
Also declared "max usable range" (18.000 for large ships) is very useful in trying to understand what happened on board KGV, when operator was obviously unable to get a constant (even weak) echo for Bismarck above 21.000 yards (
download/file.php?id=4190) and he was possibly getting a "
fluctuating echo, not reliable in practice" over 18.000 - 20.000 yards.
We will possibly never know what was 284 operator observing when constantly looking for Bismarck at about 25.000 yards (
https://www.kbismarck.org/forum/downloa ... hp?id=4164) but it is quite clear that first correct range after initial one was passed to and accepted by TS personnel at 08:53 only, possibly also due to 284 operator lack of experience and bad "understanding" between him and Gunnery Control (
https://www.kbismarck.org/forum/downloa ... hp?id=4169), but mainly because 284 at that time was not considered able to provide reliable ranges at more than 18.000 yards.
IMHO, 284 operator was mistaken by KGV's own fall of shot or by noise peak(s) at around 25.000 yards, and he continued to estimate range at that distance for some minutes.
In any case, after first salvo, fall of shot was reported short by 284 operator, This means he was actually seeing an echo attributed to Bismarck and other(s) attributed to KGV fall of shot (
https://www.kbismarck.org/forum/downloa ... hp?id=4180). Gun range was therefore increased (vs predicted range rate, possibly not yet accurate as well) and this possibly continued to happen during first minutes of battle, until 08:53, when visual observations confirmation allowed to tune AFCT accordingly.
hans
Hi Hans,
Some additional commentary found in an RN radar manual –
LOCATION
<snip>
9. Range accuracy of radar is sufficient for most warning purposes, but for accurate ranging, such as required in gunnery, sets must be calibrated, vide Chapter XII. Compared to range accuracy, bearing accuracy is not so good, varying from 1-2 deg for WS sets up to 5-10 deg for WA sets. Combined inaccuracy of range and bearing may result in an irregular plot particularly.
( a ) When a target is at extreme range and the echo is weak and intermittent.
( b ) When there is a high rate of change of bearing of the target.
( c ) Under these conditions, it may take several minutes to obtain a plot which is smooth enough to deduce the targets course and speed with sufficient accuracy.
10. Gunnery ranging sets, which are fitted with beam-switching and very accurate ranging devices will, of course, give a good plot very much more quickly.
Byron note – Type 284 had neither beam-switching, nor precision ranging panels in 1941.
<snip>
MAXIMUM RANGE
12. The first detection of a new target will not usually occur at the maximum range of which a set is capable. This is because at extreme ranges the echo is very small and often only appears intermittently. It may therefore easily be missed on several sweeps, by which time the target will have closed.
13. Without P.P.I. display it is necessary to sweep round comparatively slowly, stopping perhaps several times during each sweep to take bearings and ranges of targets already being watched. While doing this a new target which has come within radar range may have closed considerably before the sweep again reached the right bearing. The trouble is accentuated if the target is a small one, whose maximum range is not great in any case, and the closing speed is high; in fact when using an old set, such as type 272P, the theoretical chance of detection of a U-boat before it comes into sight may be nil under unfavourable conditions.
14. Sets with broad horizontal beams, such as WA sets and WC type 291, can sweep much faster without fear of missing targets than can narrow beam (WS) sets not fitted with P.P.I. In general, it pays to sweep as fast as practicable except in small ships in rough weather, vide.para.51.
15. With P.P.I. display, it is possible to sweep much faster, and this is normally done (usually automatically) so that a continuous picture is painted. This overcomes the disadvantage of narrow beams and slow sweeping and greatly improves the reliability of detection. When, however, it is desired to watch for fluctuating echoes, such as those from an aircraft or an E-boat at extreme range, over a selected sector, it may be preferable to revert to hand-training. Provided the sector is a small one, this procedure will give a greater number of chances of seeing the echo and will, therefore, increase the probable detection range. Needless to say, all round warning will be lost while the sector sweep is in force.
Byron note – Type 284 was monitored by means of an A-Scope in 1941.
Effect of inclination
16. With surface warning sets the inclination of the target makes a considerable difference to the height of echo at extreme range and therefore to the maximum range obtainable. As might be expected, better maximum ranges are obtained against targets beam on as the reflecting area is then greatest.
Byron note – According to maneuver charts, BISMARCK’s inclination from the perspective of KGV was generally bow on in the minutes prior to opening of fire on 27 May 1941.
<snip>
EFFECT OF ROUGH WEATHER AND ATMOSPHERIC CONDITIONS
Rough weather
50. The narrow beam of a centimetric (WS) set may be lifted right clear of the horizon when a ship rolls or pitches. This seriously limits the value of earlier WS sets (e.g. type 272P), especially in small ships against small targets whose echoes become intermittent or are missed altogether. T counter this in later sets either :--
( a ) The vertical beam is made wide enough to allow for all reasonable conditions, e.g. it is 20deg in type 276.
Or ( b ) the set is stabilized, as in types 271/3Q and 277.
51. Further, the swell may actually obscure the line of sight between a small target such as a U-boat and a small ship where the WS set is mounted low down. In these circumstances it is necessary with old WS sets to sweep very much more slowly than the normal rate to make certain of detecting small targets at all, which, of course, reduces the probable detection range. With modern WS sets, however, the sweep rate should, if anything, be increased. The object in all cases is to avoid coinciding with the period of the swell which normally corresponds to a sweep rate of about 4 r.p.m.
Byron note – It is not clear to me that ship motion had any effect on the efficiency of KGV’s radar. Her type 284 radar was an old unstabilized WS (“Warning, Surface”) set, to be sure. But, even considering that her closing course placed her in heavy following seas under the prevailing gale/near-gale conditions, I cannot say with any confidence whether or not it would have affected the performance of her radar. She was, after all, a very large warship.
FWIW
Byron
