How much power does a large caliber shell have when...

[Rene]

entering the water.

I remember sometime back that I read about an experiment. Someone tried to find out if a bullet fired by a rifle could kill someone when being underwater. It turned out that even a high powered rifle was not able to penetrate a significant depth.

So here is my question: what about a large caliber shell, like a 16". How close had they to hit to still retain enough power to penetrate the armor belt of a battleship?

Thanks for any informations.

Keep on modeling
Ren�
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[kennylibben]

Well they tried rifle rounds on Mythbusters and if I recall they ALL shredded upon impact with the surface of the water.

A 16 inch or something of the like, I would assume would not be so fragile... but then again I didn't expect the rifle rounds to shred either. My guess is it depends on the angle of the projection... a low angle would probably make it less effective as it would hit more surface area, similar to a belly-flop versus a well performed dive. However, hitting more surface could also mean it would slow it down enough that it wouldn't shred like the rifle rounds...

...of course I have absolutely no experience in this field, and have little experience in the practice of physics.

[Werner]

The Japanese conducted a set of experiments (named for the target ship, Tosa) in the 1920s. It turns out a conventional ship loses 1% of it's energy for every caliber of distance it traveled through the water. That means a 16-inch shell would be pretty much out of gas after travelling 133 feet. It could probably still penetrate the light supporting steel below the armor belt at half that distance.

[NAVMACS_V2]

The Japanese were so obsessed with the concept of underwater hits that they designed shells that were optimized for underwater penetration. Unfortunately for them they were significantly less effective than regular shells agains side and deck armor and underwater hits proved significantly harder to obtain than they expected.

[chuck]

The Japanese conducted a set of experiments (named for the target ship, Tosa) in the 1920s. It turns out a conventional ship loses 1% of it's energy for every caliber of distance it traveled through the water. That means a 16-inch shell would be pretty much out of gas after travelling 133 feet.

It is extremely unlikely for the shell to lose energy to water resistance in direct proportion to the distance travelled. Instead it is very likely to lose energy to water resistance in rough proportion to third power of remaining speed.

[Werner]

The Japanese conducted a set of experiments (named for the target ship, Tosa) in the 1920s. It turns out a conventional ship loses 1% of it's energy for every caliber of distance it traveled through the water. That means a 16-inch shell would be pretty much out of gas after travelling 133 feet.

It is extremely unlikely for the shell to lose energy to water resistance in direct proportion to the distance travelled. Instead it is very likely to lose energy to water resistance in proportion to third power of remaining speed.

Write to Dulin and Garzke. They filled out their thin US Battleships of WW.II with their analysis of the Tosa experiments.

[chuck]

The Japanese were so obsessed with the concept of underwater hits that they designed shells that were optimized for underwater penetration. Unfortunately for them they were significantly less effective than regular shells agains side and deck armor and underwater hits proved significantly harder to obtain than they expected.

1. If there is any demonstrated deficiency in Japanese APC shells' ability to penetrate armor it had nothing to do with the steps taken to optimze underwater trajectory. All the measures in the shell nose taken to improve underwater behavior were cosmetic, and does not effect the cap or the hardened nose. The long fuse length also does not effect armor penetration. Furthermore, shells that are deficient in penetrating hardened side armor near normal angles tend to be superior in penetrating hon-hardened deck armor at shallow angles, and vice versa. So the notion that Japanese shells were significantly less effective against side and deck armor is highly suspect.

2. The number of Japanese APC shells proven to have scored successful underwater hits along the designed lines was small (1). But the number of non-Japanese APC shells to score successfully along the lines the Japanese intended were not small. That number becomes even larger if were to accept the Kirishima theory recently advanced in an issue of Warship. So while the Japanese were unlucky, they were not barking up the wrong tree.

[Werner]

The Japanese were so obsessed with the concept of underwater hits that they designed shells that were optimized for underwater penetration. Unfortunately for them they were significantly less effective than regular shells agains side and deck armor and underwater hits proved significantly harder to obtain than they expected.

1. If there is any demonstrated deficiency in Japanese APC shells' ability to penetrate armor it had nothing to do with the steps taken to optimze underwater trajectory. All the measures in the shell nose taken to improve underwater behavior were cosmetic, and does not effect the cap or the hardened nose. The long fuse length also does not effect armor penetration. Furthermore, shells that are deficient in penetrating hardened side armor near normal angles tend to be superior in penetrating hon-hardened deck armor at shallow angles, and vice versa. So the notion that Japanese shells were significantly less effective against side and deck armor is highly suspect.

2. The number of Japanese APC shells proven to have scored successful underwater hits along the designed lines was small (1). But the number of non-Japanese APC shells to score successfully along the lines the Japanese intended were not small. That number becomes even larger if were to accept the Kirishima theory recently advanced in an issue of Warship. So while the Japanese were unlucky, they were not barking up the wrong tree.

The Japanese shells were unsuccessful because of their fusing, as noted in many other publications. Casualties on South Dakota would have been much higher if the Japanese shells were not fused so long (to take advantage of the diving technique, which lengthened the time from fuse initiation to the calculated hit point 10 meters or so inboard). As a result, shells were observed to pass entirely through South Dakota's narrow superstructure and explode well distant on the unengaged side.

The work quoted from Warship International, if true (and I tend to believe it, because it is consistent with my other theories on US Radar) only proves the Japanese wasted their time and effort designing a shell for an extraordinarily rare circumstance, when conventional shells were just as, if not more dangerous, under identical circumstances.

Perhaps the "diving shell" is the Japanese equal to the Russian "round battleship", or Steven's Floating Battery. Even great powers can make great mistakes.

[chuck]

1. Long fusing does not hamper armor piercing.

2. North Dakota would not have sunk or have been critically damaged even if every Japanese 14" shell observed to hit successfully exploded inside the ship. There having been no underwater damage or any hits to the citadel.

3. Contrary to what you seem to say out of what appears to be pure reflex, the Warship International's Washington/Kirishima article makes the case that shorts resulting in underwater hits are not rare at all - having occurred 6 times, or once for every 2-3 claimed direct hits, in just the one engagement mentioned. Furthermore since the article claimed the Kirishima was not scuttled but actuall sunk, and not by any torpedoes either, one must therefore presume that it was the underwater shell hits that put the Kirishima in "sinking" condition because it requires admission of water to put a ship in a condition susceptible to sinking, or even to put the ship in a state requiring counterflooding the engine room to remediate. Consequently the article, if its claimes were true, would seem to make a rather convincing case that underwater hits are quite likely, and moreover hit for hit they are also quite likely to be much more decisive then direct hits, and therefore are well worth the effort to make them more frequent.

[Tim Jacobs]

An interesting similar event, but with a very different ending, would be PoW vs Prinz Eugen and Bismarck. Two 8 inch rounds hit PoW below the waterline in the aft sections, damage not seen until the ship was refueling after the engagement. More importantly, when the ship was drydocked in Rosyth, it was discoved a 15 inch shell had hit and penetrated the ship 28 feet below the waterline near the starboard diesel generator room. It didn't explode.

One of PoW's officers, LCDR Brooke is quoted as saying, "A 2000 lb shell detonating in very close proximity to both oil fuel and diesel oil could at best have started a major fire and blown out the side of the ship at that point. "Y" turret was only yards away, and at worst there could have been an explosion in too faithful emulation of the Hood."

In that engagement, PoW was hit by 3 x 15 inch, one of which was below the waterline, and 4 x 8 inch, two of which were below the water line.

citation: King George V Class Battleships, V. E. Tarrant, pgs 60-62, 83-84

If the German fuse had detonated, PoW could have been lost or at least severely damaged.

Following Chuck's train of thought, the proportion of below-the-waterline hits to direct hits does seem to be a lot higher than one would expect, though admittedly, it's a very small sample size.

[Bill Jurens]

Predicting the trajectory and residual velocity of a projectile travelling underwater is far from a straightforward task. Generally, unless specially designed for water entry, the projectile passes through three phases after impact: a very short one -- consuming perhaps 10-15 calibers of travel -- where the bullet remains more-or-less nose forward and drag is quite small due to cavity formation, another very short one -- perhaps ten calibers long -- where the projectile is typically rotating to a base-forward postion, and a final long section where the projectile continues in a base-forward mode, often with considerable 'wobble'.

As a rough rule of thumb the projectile velocity drops to about 90% of impact velocity in the first 15 calibers of underwater travel, further decreases to about 35% of it's impact velocity during the next 10 calibers of travel, i.e. after 35 calibers total travel, thereafter dropping to zero velocity (or nearly so) by the time 40 calibers is reached.

The general shape of the trajectory represents a portion of a circle, with a small straight section near the impact point. Shells which ricochet can often reach fairly substantive depths before re-emerging again; a richochet does not mean that the projectile bounces off the surface of the water, merely that the curvature of the trajectory, and the residual velocity, allow it to come back to the surface again after a short underwater travel. For an angle of fall of 15 degrees, this amounts to a depth of about two calibers. In such cases, a lot depends upon the slope of the surface being struck; the average wave slope typically being something in the vicinity of 10 degrees, and the usual ricochet angle being about 12 degrees, this means that ricochets are for angles of fall ranging from about 2 through 22 degrees from the global horizontal.

Bill Jurens

[Werner]

1. Long fusing does not hamper armor piercing.

2. North Dakota would not have sunk or have been critically damaged even if every Japanese 14" shell observed to hit successfully exploded inside the ship. There having been no underwater damage or any hits to the citadel.

3. Contrary to what you seem to say out of what appears to be pure reflex, the Warship International's Washington/Kirishima article makes the case that shorts resulting in underwater hits are not rare at all - having occurred 6 times, or once for every 2-3 claimed direct hits, in just the one engagement mentioned. Furthermore since the article claimed the Kirishima was not scuttled but actuall sunk, and not by any torpedoes either, one must therefore presume that it was the underwater shell hits that put the Kirishima in "sinking" condition because it requires admission of water to put a ship in a condition susceptible to sinking, or even to put the ship in a state requiring counterflooding the engine room to remediate. Consequently the article, if its claimes were true, would seem to make a rather convincing case that underwater hits are quite likely, and moreover hit for hit they are also quite likely to be much more decisive then direct hits, and therefore are well worth the effort to make them more frequent.

I tried to make my point simple, but...

1. The long fusing hampered Kirishima in that the shells striking the superstructure passed a long way (I have the impression of 100 yards or so) through South Dakota's superstructure before detonating. Obviously, the cumulative effect of the entire superstructure was only sufficient to begin the fusing process which the fuse regarded as the the shell striking the water.

When you and I have discussed similar issues in the past, I notice you only consider hits within the citadel of the ship, when most of the battles since 1905 have shown how important C3I features in the superstructure are for the ship's ability to fight back, and therefore survive. Bismarck was pummeled into a quite useless shape before her citadel was pierced. Even South Dakota was a "soft kill" in this engagement simply because her electrical supply to radar and fire controls was interrupted for a few minutes. After-action comments regarding long delays on Japanese AP shells are not confined to this engagement.

It is interesting that Kirishima appears to have greatly overestimated the range to target. Perhaps the targeting officer thought she was a smaller vessel.

2. North Dakota was not present at the battle, having been expended in experiments in the 1920s. I don't know whether you mean North Carolina's sister ship Washington which was undamaged at all in the engagement, or South Dakota, which in any event took (as I recall) all of her damage above the waterline. Unlike you, I cannot speak to the "commonness" of diving hits when you consider the engagement was extraordinary, with the 16 inch rounds fired from 10,000 yards down. I tend to think of capital ship engagements would occur at at least twice this range, with 15,000 being a satisfactory range for penetrating hits on both sides (speaking archaeologically, of course. Each player had his own preferred range which conferred a decisive advantage).

3. I don't know what to say about the ratio of direct penetrating hits and "diving shell hits", as opposed to near misses and so on. I will wait for more analysis from the experts.

What it seems is that we need to increase the effective width of a target when accounting the probability of hits and likely penetrating hits below the waterline. My question right now is why did the Japanese bother with all this when the net effect was to make the fuse time so long as to reduce damage except when the diving effect is fully in play.

It is possible this was an exceptional engagement, especially considering the quantity of commentary from Kirishima about attempting to maintain stability; it is unclear to me whether the concern was in list or pitch, since there are comments as to the entire fore half of the ship being missing. Perhaps a magazine separated a vast portion of the fore quarter of the ship and the effort was to stop her from submarining. In any event, since we have little other comment regarding loss of stability in the other Japanese battleship surface engagements, I cannot make any inferences. Being totally ignorant of the Italian experience, it might be an illuminating time to investigate the battles of the Mediterranean.

A final comment: the new data only reinforces the efficacy of unit machinery disposition with no centerline bulkheads, and where possible auxiliary machinery rooms separating engine plants.