Discussion about spotting ranges

[Kaiser Kirk]

I don't think the 2 extra guns are worth it. A ~1" thick deck is sufficient to defeat 15cm shells at ranges I'd consider feasible in Nverse 1925.

I rather strongly disagree. 1918 Firecontrol gives ranges out to 24k.
The USN's Omaha's 6" gun is listed as
20,800 yards (19,020 m) --- 1.5" (38 mm)
23,600 yards (21,580 m) --- 2.0" (51 mm)
As a caution - these were 1942 curves on a 1923 gun.

50mm is hard on a cruiser, and only useful at the outer edges of the range, but even the 35mm deck isn't 'proof' much past the old FC limit of 18k.  However, considering the pen # very well may be for later shell designs, the 35-38mm range is certainly reasonable.

As for the two extra guns... heavy manuevering degrades targeting. If the task is screening the line against a New Swiss DD charge, then broadsides may be useful. If the task is independent cruising, it's more debatable.

[P3D]

You won't be able to spot the fall that far out.
The rule of thumb for effective firing range is 1km for every 1cm of caliber.

[ctwaterman]

You won't be able to spot the fall that far out.
The rule of thumb for effective firing range is 1km for every 1cm of caliber.

So in this case a 15cm shell can only spot fall of shot out to 16,500 yards... effectively.... hmmmmm just usint the rule of thumb.   But it the rule of thumb meant 1 mile per cm... then the rule would be...26,400 yards.....????

So who's Thumb are we using...???

[Sachmle]

Honestly, I thought it was 1,000yds per cm of caliber, so I'm going to figure P3D's number is correct.

[Kaiser Kirk]

You won't be able to spot the fall that far out.
The rule of thumb for effective firing range is 1km for every 1cm of caliber.

Interesting. Well that would change things.

The discussion of Japanese 8" guns on Navweaps has the following

Large dispersion patterns were a problem with these ships during their early service life, with Takao in 1933 reporting patterns of 483 meters (530 yards) at a mean firing range of 19,300 meters (21,100 yards).  In a target shoot against the old Aso (ex-Russian Armored Cruiser Bayan) in 1932, the cruisers Nachi and Myoko repeatedly straddled at ranges between 15,800 and 22,300 meters (14,450 and 20,390 yards) yet failed to score a single hit because of dispersion patterns of about 350 meters (380 yards).

Much effort was put into reducing dispersion, with the Nachi class in 1936 achieving patterns of 280 to 330 meters (306 to 360 yards) at ranges of 20,000 to 22,000 meters (21,870 to 24,060 yards).  The Japanese also introduced electro-mechanical aids, such as the Type 98 (Model 1938) Gunfiring Delay Installation which consisted of a "trigger time limiting device" which reduced the time of firing to less than 0.2 seconds after the circuit was made and a "firing time separator" which produced a lag of 0.03 seconds between the firing of each gun in a turret.  This latter device was to make the shells leave each gun barrel at slightly different times, thus reducing their mutual interference in flight.  These devices reduced dispersion by about 10-15%.  Patterns for the 10-gun cruisers were reported as being very small at the Battle of Samar in 1944.

6) According to "Japanese Cruisers of the Pacific War," the average maximum range for the 10-gun cruisers for daylight actions increased from about 16,840 yards (15,400 m) in 1924 to greater than 21,870 yards (20,000 m) by 1937 and the estimated hit projection increased from 3.0% at 21,870 yards (20,000 m) in 1930-34 to 6.0% in 1935-1940.  The actual percentage of hits achieved during the war was much lower than these figures, a not unusual experience.

Which would seem to indicate that they certainly expected to be fighting out the 20,000yard limit the rule of thumb would allow for, but that they were also expecting to fight past that.  Part of that is shell form, part is gun elevation, but spotting would remain an issue.  What changed in their Fire Control methods to allow them to expect to control past the rule of thumb splash range?

hmm thinking about it, the rule of thumb is beneficial to my designs with their range-limiting antiquated casements, and a better argument for 18cm for anti-DD work :)

[Sachmle]

6) According to "Japanese Cruisers of the Pacific War," the average maximum range for the 10-gun cruisers for daylight actions increased from about 16,840 yards (15,400 m) in 1924 to greater than 21,870 yards (20,000 m) by 1937 and the estimated hit projection increased from 3.0% at 21,870 yards (20,000 m) in 1930-34 to 6.0% in 1935-1940.  The actual percentage of hits achieved during the war was much lower than these figures, a not unusual experience.

That would be a neat trick anyway since of the "10-gun cruisers", the Nachi class didn't enter service until 1928-29 and the Takao didn't enter service until 1932. How did they derive their effective range in 1924 when they were just laid down in 1924. In 1932 they had their 200/50 swapped out for 20.3/50s, most likely helping with the dispersion problem.

[Kaiser Kirk]

I presume when designing the vessels they had some expectations as to what ranges they would be fighting at and thats what the quote refers to.

The quotes come from Navweaps discussion of the latter gun. There is a reduction in dispersion discussed , but the main effect seems to have come from the delay coils.  The USN also found that with their older dreadnoughts, delay coils were useful in reducing dispersion. I believe the issue was simply the guns were mounted to close together in an effort to keep turret & barbette size down. One of the British CL classes had a longer mid gun in a different attempt to address the problem.

[Guinness]

Actually, the RN's 6 inch Marks XXII, XXIII, and XXIV had the middle gun set back relative to the outer guns to reduce interference between projectiles in flight.

I believe in the quote you guys are referring to we're talking maximum range of guns in the context of whatever the maximum elevation was, not at what distance the fall of shot could be spotted.

[Kaiser Kirk]

Whoops- I knew there was a length diff, had it backwards.

As for the IJN weapons, the elevation on the 1932 twin mounts ranged from 40 to as high as 70, with ranges out to 32,000yds.
The original 1923 guns on Furataka had an elevation of 25 degrees and a max range of 26,250 at that elevation.

So I would presume the ranges indicated in the quotes are the expected maximum fighting ranges. It's the bit where they were straddling at 22,300 meters in firing practice (which I presume means they can spot there), the reference on the Nachi working on dispersion between 20-23km, and then the reference to average maximum range for daylight actions increasing to 'greater than' 20,000m... all of which would seem to indicate expectation of combat and fire control, thus presumably spotting, past the 1km/cm rule of thumb, but not greatly so.  Perhaps it's the larger diameter optics, wider base rangefinders, or something particular to the IJN, or perhaps the rule of thumb needs a bit of tweaking as 22,300m is 10% greater.

[P3D]

A rule of thumb is just that - in this case saying that hit probabilities in combat would drop rapidly beyond some range around 1km/1cm. The Japanese might have thought that hit probabilities would still be acceptable at 22,300 meters, and the cutoff was somewhat further.

Keep in mind that the maximum range of the gun is not the expected firing range. She ship is rolling constantly, and you need a few degrees of elevation to compensate for that in continuous aiming.

The actual combat records for long-range cruiser gunnery are far from stellar AFAIK, with very low hit probabilities - agreeing with the rule of thumb.

Before someone asks, unfortunately I don't have any reference on the latter (long-range hit probabilities).

[Guinness]

I suspect the Japanese might have been spotting by air.

They, like several other nations including Britain, btw, had pretensions of using 6" and 8" guns for barrage AA fire, which is why some mounts had such high elevation. It wasn't to increase range for surface fire.

[Kaiser Kirk]

Yes, the high elevations were likely for AA use, which many nations dabbled in and all found rather ineffectual on the large guns.

Air spotting would make sense for extra the ranges and might be the best explanation.