Naval gunnery accuracy - question for M. Jurens

[Francis Marliere]

Gentlemen,

In a Mr Jurens's now well-known article (http://navweaps.com/index_inro/INRO_Hood_p4.htm), there is an equation that computes hit chances of naval artillery :

Ph = 10(E-TX)

Where:

Ph = Percentage of hits
K = Percentage of hits at maximum range of gun
E = 2.00
T = 0.02 - (0.01 Log K)
X = Percentage of the maximum range of gun

The hit chances are here a function of range between the shooter and target, and the maximum range of the gun. However, we all know that hit chances heavily depends on other parameters :
- quality of fire control
- assistance of fire-control radar or aircraft spotter
- visibility
- sea state
- size, speed and manoeuvers of target
etc.

Could you please precise the influence of these factors in the shooting ?

Best regards,

Francis Marliere

[Bill Jurens]

That's probably a book length topic. :-)

The equation quoted was for U.S. fire control in the 1920s, no aircraft, good visibility, battleship-sized target, and minimal maneuvering.

The Naval War College and other sources developed much more complex equations later on, which degraded the hit percentage by specific amounts depending upon conditions.

Bill Jurens

[Francis Marliere]

Mr Jurens, does the INRO article you co-authored with Mr Fischer deals with that ?

In an old thread, you spoke of "Maneuver and Fire Rules" which were used by the Naval War College. Could you please tell me more about that ?

Best regards,

Francis Marliere

[Brad Fischer]

Mr Jurens, does the INRO article you co-authored with Mr Fischer deals with that ?

In an old thread, you spoke of "Maneuver and Fire Rules" which were used by the Naval War College. Could you please tell me more about that ?

Best regards,

Francis Marliere

I cannot speak for the latter but yes, the hit probability model that was detailed in WI 43-1 deals with this and would be relevant for some specific circumstances. Generally, the typical main battery target was maneuvered from 20-40° off base course at speeds in the 20kt range (speeds varied as they would in real combat and were as high as 28kts). The model would be representative of a USN Battleship equipped with the Mark 8 radar engaging a target on a more or less parallel course that is maneuvering to throw off gunfire. In other words it represents a typical battle line action.

It would be much less representative of fine target angles, “radical” maneuvering and firing ship degradation due to damage. The first two variables being more indicative of the numerous light unit actions in 1942 and 1943 in the South Pacific. Of course with any mathematical model it’s more of a theoretical exercise and is subject to the limitations of the data it’s derived from hence a need for a more comprehensive modeling in the form of real time simulation.

Brad Fischer

[Bill Jurens]

The Maneuver and Fire Rules were developed by the U.S.N. Naval War College about 1920. They were re-issued fairly regularly -- about once every five years or so -- and were in use until about 1947. These rules -- a complete set is about 400 pages long -- were specifically designed to model surface gunnery and torpedo actions. Overall, the mode of operation was quite similar to the Fletcher Pratt Naval Wargame except that the official rules used the results of actual target shooting etc. to model the gunnery problem and used -- at least for USN ships -- accurate models of the armor suite.

The rules specified a basic rate of "Hits Per Gun Per Minute" for each major gun type vs range. The raw figure could be modified slightly to account for variation in conditions, e.g. the HPGPM might be lowered 10% if the ship were in funnel smoke, or 5% if the sea state was above three, or 15% if the target was directly 'up-sun' etc. etc. The size and maneuverability of the target was taken into account as well. Similarly, the raw figures could be increased to account for air spot, etc.

For each salvo -- the move interval was three minutes -- the HPGPM value was calculated, the number of hits computed, and the effectiveness of the target was degraded. Ships were each assigned a 'lifetime', usually expressed in terms of 14" penetrating shell hits.

A very comprehensive summary of the Maneuver and Fire Rules was published in Alan Zimm's 'Battle Stations" wargame about thirty years ago, but so far as I know the precise rules have not been reproduced elsewhere. The Naval War College has copies of the M&F Rules on file in their libraries, but I don't think they have facilities to make copies. 400+pages is a lot of paper...

Hope this helps...

Bill Jurens

[Bgile]

I loved that game. I contacted him with the idea of reprogramming it in C, but unfortunately I didn't get anywhere and it died.

[dunmunro]

I loved that game. I contacted him with the idea of reprogramming it in C, but unfortunately I didn't get anywhere and it died.

He also wrote a computer game:

http://www.mobygames.com/game/dos/action-stations

Which I have buried somewhere.

As I recall, I found the game interesting but the hit accuracy was way too high, and so produced very unrealistic results.

You can download it from here:
http://www.hotud.org/component/content/ ... n-stations

[Bgile]

I loved that game. I contacted him with the idea of reprogramming it in C, but unfortunately I didn't get anywhere and it died.

He also wrote a computer game:

http://www.mobygames.com/game/dos/action-stations

Which I have buried somewhere.

As I recall, I found the game interesting but the hit accuracy was way too high, and so produced very unrealistic results.

You can download it from here:
http://www.hotud.org/component/content/ ... n-stations

Oops that was what I was referring to. There were a few problems, including that if one of your ships was hit with a large number of secondary battery hits you could lose control of it. Overall it was pretty good though, especially for it's time.

[Bill Jurens]

There was a 'pencil and paper' version as well, which came out earlier than the computer version. This is still useful for research into the M&F Rules because it described the hit percentage equations in some detail. I don't think the computer version did that.

Bill Jurens

[Bgile]

There was a 'pencil and paper' version as well, which came out earlier than the computer version. This is still useful for research into the M&F Rules because it described the hit percentage equations in some detail. I don't think the computer version did that.

Bill Jurens

No, it didn't and that confused me at first because I was thinking you were referring to the computer version (I'd forgotten it was called "Action Stations") and I of course didn't remember seeing the equations.

[Francis Marliere]

Gentlemen,

sorry to post a new question on this topic, but there is another point I would like to discuss. As already said, the equation in the article was Ph = 10(E-TX) where X is the maximum range of the guns. I understand that the maximum gun range is achieved at 45° elevation. What about guns, such as German 38 cm (and many others) that cannot elevate to 45° ? How can I compute or guess theorical maximum range for these guns if I only their effective range at xxx degrees ?

Thanks for your help,

Francis Marliere

[lwd]

One way is to look for the use of the same gun in another mounting. For the German guns you might look at their use as coastal batteries for instance. For some of the British battleships look for the ones with the upgraded turrets. Also there may be some data from test firing where their wouldn't necessarily be the elevation limit. Lacking that you can get ballpark numbers by extrapolating and/or comparing to other similar guns. For instance of you have elevation vs range data for say every 5 degrees up to 40 degrees extrapolating to 45 should get you pretty close. If you only have data for say 10 degrees, 20 degrees, and 30 degrees on the other hand the estimate for 45 degrees is likely to be considerably more questionable.

[tommy303]

Generally speaking, range tables are usually available for most guns, although one might have to do some digging to find those listing absolute maximum ranges. These would normally be compiled from test firings by the manufacturers. On the whole, when talking of battleship guns, absolute maximum ranges are usually obtained at elevations slightly more than 45* since these powerful guns were capable of firing a shell to such great heights that it was travelling for a portion of its flight in very thin air with much reduced friction. The actual amount of range increase per degree of elevation is not linear, however, (if I have the right term), and at higher elevations the increase is much less per degree than at shorter ranges. For this reason, 30-40* was considered adequate, the small increase obtained at 45* was not considered worth the complications of designing and producing turrets capable of greater elevation. In the case of the Bismarck's 38cm the maximum range was 36,520m at 30*, while the absolute was 42,000m at 52* using the standard naval AP shell and powder charge.

[Francis Marliere]

Gentlemen,

I have ordered and read the article 'Fast Battleship Gunnery'. While wonderfull, the article opens the way for more questions.

First, the authors talk about a spreadsheet to download in INRO's website. Unfortunately, I couldn't locate that file. Could you please tell me where it is ?

The article deals with USN fast battleships gunfire. Are things different for other warship types (cruisers, destroyers, etc.) and / or other navies (RN, DKM, etc.)? In other words, is it possible to extrapolate from the article hit chances for a USN cruiser or a foreign battleship ?

I may be mistaken, but I think that in some night battles (Tassafaronga especially), fire control radar didn't perform well and locked on shell splashes rather than on the target. If that did really occur, how often ?

Thanks for your help,

Francis Marliere

[Bgile]

I'm curious ... the most recent article was called "Fast Battleship Gunnery during World War II: A Gunnery Revolution" and was divided into Part I and Part II.

Part I was in Warship International Vol. 42 Issue 2.
Part II was in Warship International Vol. 43 Issue 1.