15/42 versus KM 38cm

[dunmunro]

1) check the dates of issue of the two documents and decide which one Leach would have read before the action.
2) This is irrelevant

Irrelevant to you perhaps.

Fact is both documents consider 15"/L52 as less powerfull than the 25 years old British 15"/L42, which is very interesting to say the least.

And Leach certainly knew the capabilities of the British gun .

The 15/42 fired a heavier shell at lower MV and at shorter ranges the 38cm does have better penetration, but at longer ranges the situation reverses. Overall, there's not much to choose between them. I'm fairly certain that the RN thought that the European guns had light shell/high MV characteristics.

[alecsandros]

1) check the dates of issue of the two documents and decide which one Leach would have read before the action.
2) This is irrelevant

Irrelevant to you perhaps.

Fact is both documents consider 15"/L52 as less powerfull than the 25 years old British 15"/L42, which is very interesting to say the least.

And Leach certainly knew the capabilities of the British gun .

The 15/42 fired a heavier shell at lower MV and at shorter ranges the 38cm does have better penetration, but at longer ranges the situation reverses.

That's true,

the better penetration comes mainly from the 10% higher initial muzzle velocity of the German gun.

this gives a flatter shell trajectory, hence a larger hitting space.

And , yes, at longer ranges (>20km), the British 15" gun has better horizontal perforation characteristics, precisley because the shells have a steeper angle of fall, the gun being closer to it's maximum ballistic range.

===

[Dave Saxton]

And , yes, at longer ranges (>20km), the British 15" gun has better horizontal perforation characteristics, precisley because the shells have a steeper angle of fall, the gun being closer to it's maximum ballistic range.

Hmmm. I know some pentration tables list about 165mm at 32,000 yards with a angle of fall of 37* for 15"/42 firing the 6crh windscreen shell. And that these same tables list the 4crh windscreen shells used on Hood to penetrate almost 200mm at the max range of 29,000 yards ( 26.5km). However, we know that these predictions are WRONG.

We know from British firing range testing that no British BB shell could penetrate more than about 5" deck at any battle range of less than 32,000 yards. This is a fact. The deck penetration is about the same as the German 15" out to 32,000 yards. How could the penetration tables and math models be so wrong? It is because they don't take into account the head shape of the main body of the shell which is most important, among some other factors.

The newer KM 38cm has superior or equal penetration performance to the older 15"/42 at all battle ranges vs both vertical and horizontal armour.

In the British documents comparing possible performance between the German and British 15" before and right after the Hood's loss; the British also assume that the German 15" shell was 1600 lb.

[alecsandros]

We know from British firing range testing that no British BB shell could penetrate more than about 5" deck at any battle range of less than 32,000 yards.

... I don't want to quibble, but at 25km, German shells falls at 23.7*. British shell falls at nearly 40* (assuming standard charges). This is a substantial difference, and it probably affected perforation of horizontal armor. [GKDOS 100 mentions 120mm perforation; theoretical value of perforation for British shell is 175mm - which even if downsized by 10% would still stay around ~ 150mm]

What should be noted however, is that the German shell can be delivered at a larger range, where the British shell can not reach (36km vs about 28km).

[alecsandros]

In the British documents comparing possible performance between the German and British 15" before and right after the Hood's loss; the British also assume that the German 15" shell was 1600 lb.

Indeed,
one of the boards of inquiry also considered Bismarck's guns muzzle velocity up to 3150fps, and definetely not below 2800fps. With those values, the figure of 13000/15000 yards IZ for Prince of Wales is simply absurd... Perhaps they grossly overestimated the stopping power of their own (new) cemented armors ?

[Dave Saxton]

...but at 25km, German shells falls at 23.7*. British shell falls at nearly 40* (assuming standard charges). This is a substantial difference, and it probably affected perforation of horizontal armor. [GKDOS 100 mentions 120mm perforation; theoretical value of perforation for British shell is 175mm - which even if downsized by 10% would still stay around ~ 150mm].

That would be the case of all the other factors are the same, such as the oblique striking angle performance of the British shell being the same as the German L/4.4. However, there's a significant difference of performance at oblique striking angles.

The oblique striking angle performance of the L/4.4 may be the main factor in the Bismarck shell penetrating to the Hood's magazines, rather than extra high muzzle velocities.

[alecsandros]

That would be the case of all the other factors are the same, such as the oblique striking angle performance of the British shell being the same as the German L/4.4. However, there's a significant difference of performance at oblique striking angles.
.

... agreed, but let's not forget that the British 15" shell would fall at 40*, and had a mass of 880kg (10% more than the German shell). Striking velocity would be pretty similar at 460m/s for both shells. And, in perforation of homogenous armor, projectile mass is more important than in perforation of cemented armor.

At 25km (27500 yards), GKDOS predicts 120mm of horizontal armor perforated, and my guess is that the British shell would perforate more than that.

British 1945 trials that you mentioned, were almost certainly done using super-charges, so the 15" shell fired from the L42 gun had a larger range, but consequently a smaller angle of descent at same range as the non-super-charged shell...

P.S.: An example of 15"/L42 doing well is the hit made by the HOOD on Dunkerque's main turret. The firing was done at only 15-16km distance, so descent was not ideal, yet the shell took out half the turret... Admittedly, the turret was protected by cemented armor, but nonetheless, the case shows that the shell behaved well in poor obliquity conditions...

[Dave Saxton]

I'm using R&R's published ballistic data which state that the 15"/42 can reach 32,000 yards without supercharges at 30* elevation when using the 6crh windscreen (1938lb) projectile. If I recall correctly at that range the 6chr shell is also falling at about 40* and striking at about 440m/sec.

If all British battleship shell of WWII perforate less than 6" at ranges of less than 32,000 yards (essentially 30km) this pins down the max possible deck perforation at 30km at being no greater than more or less 150mm. I have graphed the curve of all the WWII 15" guns for deck penetration vs range several years ago and applying the curve to a point of 150mm at 32k yards (would be approaching 160mm at 32820 yards) it infers a penetration of less than 120mm for the 15"/42 at 25km. I would expect the 4crh windscreen projectile to have slightly more deck penetration between 25,000 yards and max range of 29,000 yards than either the 6crh British projectile or the German projectile. But none of this 200mm at 26.5km stuff.

[Dave Saxton]

If we compare the Hood's 15"/42 guns, which used the 4crh shell, to Bismarck's 38cm at the battle ranges of Denmark St. in terms of belt penetration, there really is a stark difference (13.5" vs 18" at 20k yards). This could have profound influence on precieved IZ by the British of both Hood and KGV class if they assumed that the two guns were fairly close in belt penetration performance, and performance at oblique striking angles.

[alecsandros]

If we compare the Hood's 15"/42 guns, which used the 4crh shell, to Bismarck's 38cm at the battle ranges of Denmark St. in terms of belt penetration, there really is a stark difference (13.5" vs 18" at 20k yards). This could have profound influence on precieved IZ by the British of both Hood and KGV class if they assumed that the two guns were fairly close in belt penetration performance, and performance at oblique striking angles.

... KGV's belt was 14.7" near magazines and 13.7" near machinery.

So perforation of the belt from 15"/L42 was possible up to 17000yards / 20.000 yards respectively.

How on earth they considered the German guns so weak as to perforate the belt near magazines at only 13000 yards, is very shady.

NOt even the revised document, published after Hood's demise, was not so much better: it showed KGV class belt as immune at ranges over 15000 yards. Again, this implied Bismarck's artillery was weaker than Hood's !

[RNfanDan]

Of course, German 15" projectiles WHICH FAIL TO EXPLODE don't factor into the open-range tests now, do they?

One can PENETRATE all sorts of armor plate just fine, but if that's ALL it does, i.e., when it fails to detonate (as in Prince of Wales' case), its value deteriorates to that of a heavy wrecking ball strike.

Quite a significant percentage of German shells at DS were non-detonating, both 15" and smaller calibres.

It was fortunate for Bismarck that the shell which struck Hood a fatal blow was NOT the one which was removed intact from Prince of Wales in drydock, later; random chance that its loading order just happened to be further down than the "hot" one that worked for Hood....

[tommy303]

Quite a significant percentage of German shells at DS were non-detonating, both 15" and smaller calibres.

One can say the same thing about British shells in the same battle, with one (33%) out of three detonating and 3 (43%) out of seven German shells hitting PoW doing the same. However, in neither case does the reason for failure to detonate receive much attention, and no one is certain if a shell subsequently burst outside of the ship or not in most cases.