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Dispersion Naval Guns


Does anyone have information on the dispersion of any Italian naval guns? It's usually given as either a % of range or as meters/yards at a specific distance.


Active Member
You may refer to this post of mine with regards to the 381/50 guns: https://comandosupremo.com/forums/i...ticle-on-the-early-condottieri.955/#post-3900

This table (source: Erminio Bagnasco, Augusto De Toro, "Le corazzate delle classi Conte di Cavour e Duilio (1911-1956)", Parte 1, Storia Militare Dossier n. 47, gennaio 2020) provides several data, included the dispersions, of the 320/44 and 381/50 guns in two different years of training:

This table (source: Giuliano Colliva, "Questioni di tiro... e altre", Bollettino d'Archivio dell'Ufficio Storico della Marina, settembre 2003, dicembre 2003 and marzo 2004) gives the dispersion of the medium calibers, measured as the lenght of the strip into which the 50% of the shells fell, measured as a percentage of the firing range of 17,500 m:


Interesting. I don't see where they recorded the horizontal dispersion.

Thank you, though.
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"Disp. long.": dispersione longitudinale = dispersion in length
Yes it gives the longitude. But it doesn't say (I don't read Italian) how far off to either side of the longitudinal line 50% of the shots fall. I called it "vertical" dispersion but should have said horizontal. I'll edit my reply.


AFAIK the measure that you are looking for is the "apertura long." (apertura longitudinale), but I am not 100% sure.
I'm thinking that's where the other 50% of the shells fall in longitude. But keep me posted. You obviously have better luck than me.


I have been able identify some of this table's information:


Line 1: % of salvo: Percentage of salvo utilized.
Line 2: culpi sol bers.: % of hits on the target (9.0). The target was probably the San Marco. The target was not moving. It's likely 9.0 was transposed with 2.6 in the next column and so indicated by the penciled correction.
Line 3: Ritmo medio (seconds): Number of seconds to reload the gun ( 48)
Line 7: disp. long. (m): Total dispersion from the longitude (620 meters) (100% of horizontal dispersion)
Line 8: Apertura long. (m): Total dispersion in longitude (769)

Thus, in this 320mm gun test, the shells landed in a roughly 700 meter diameter circle with 2.6% hits. That's about a 1% chance of hitting a nonmoving destroyer, 2.6% on a light cruiser, and 4.7% on a battleship.

Lines 4, 5, and 6, I don't know.
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line 1 is not percentage of guns utilized, actually idk what mean but could be like useful salvos, probably salvos on target
line 4 possibly shell fall away from the salvo
line 5 possibly shell not fired


Active Member
The table comes from Appendix 1 of the book, which does not provide an explanation of the data. I had to check the whole text of the book and on page 93 I found these information:
- apertura longitudinale: distance, measured on a line parallel to the line of fire, between the shortest [nearest] and the longest [farthest] shot of a salvo;
- dispersione [written without the adjective "longitudinale"]: twice the aritmethic mean of the deviations of the shots from the center of the salvo.

For a better understanding of these technical details I think you should refer to the English language edition of the book, guesswork won't reach any definitive conclusion.

PS I have deleted my previous messages with imprecise information.


New Member

I can offer some clarification to some of the terms used here.

  1. 'Salve Utili' is 'Effective' or 'Useful' Salvoes - the % figure refers to the percent of salvos in the shoot with a dispersion of 1% or less of the range.
  2. 'Colpi sul Bersaglio', as already noted here, is rounds on target.
  3. 'Ritmo Medio' is the average rate of fire of the shoot, or, rather, the average firing cycle.
  4. 'Colpi Anomali' or 'irregular/abnormal shots' is actually not clearly defined by any of the books I have, so I can't do much more than speculate, but it seems to be irregular rounds in terms of dispersion/fall of shot.
  5. 'Colpi Perduti' is 'lost/failed rounds' - this refers to rounds that failed to fire for one reason or another. Which was a considerable issue during the early work-up and calibration of both gun systems, as seen in the table above, though much less of an issue by 1940.
  6. 'Dispersione Longitudinale' is 'Longitudinal Dispersion'. This is taking the average fall of shells away from the MPI (mean point of impact) of a salvo and doubling it, which gives you your average salvo dispersion in range.
  7. 'Apertura Longitudinale' is 'Longitudinal Spread'. This one is a term who's exact significance is somewhat unclear with me. The definition given is, as DrG indicated above, the distance measured between the shortest and longest shots of a salvo. This would tend to make one think of a discussion of the maximum spread seen in any salvo of the shoot.
It is worth noting, however, that in the English-language version of Bagnasco & de Toro's book on the Conte di Cavour and Duilio-classes, they include a note that does not exist in the Italian monographs with the same table, which states; "Note: In these tables 'spread' relates to the opening salvo, while 'dispersion' covers the following salvoes." In light of that, I suspect that 'apertura longitudinale' is referring to the maximum spread of the opening salvo, while 'dispersione longitudinale' then covers the average dispersion of the salvoes in the rest of the shoot.

This, to use this as an example;
Thus, in this 320mm gun test, the shells landed in a roughly 700 meter diameter circle with 2.6% hits. That's about a 1% chance of hitting a nonmoving destroyer, 2.6% on a light cruiser, and 4.7% on a battleship.

One could fully describe this as;

"In the 320mm gunnery exercise carried out at 1st charge and a range of 23,600 meters, 44% of salvoes had a spread of ≤1% of the range, and average firing cycle was 48 seconds (1.25 rpm). 12% of shots failed to fire, while 4.5% of shells behaved irregularly. Spread of the opening salvo was 769 meters in range, while average dispersion for the exercise was 620 meters. Overall hit rate against the target was 2.6%."

*edit - apologies, realized I was missing a rather important 'not' in the comment on the term 'colpi anomali'
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Staff member
Excellent clarification. Grazie!