1935 paper on British BC design, gun choice, attack range

[alecsandros]

A good read, IMHO:

http://www.hmshood.org.uk/reference/off ... 1-9387.htm

"F.A. Buckley […]
D.T.S.D. for D. of T.D.
2.8.35 2.8.35

The question of what protection and speed is required in a new battle cruiser is discussed in this paper.

2. Following the principle worked to in the case of the HOOD, a battle cruiser’s protection should be the same as that of a battleship. The protection must, therefore, depend on what the decisive fighting range is to be, assuming an equal calibre of gun on either side. The Battle Instructions state 12,000 – 16,000 yards.

3. The argument for increasing this and thereby saving weight is that, with modern control arrangements and air spotting, really effective fire can be produced at greater ranges, say 18,000 – 20,000 yards.

The argument against any increase is that, when and if the means of air spotting are destroyed with possibly the finer fire control arrangements, effective and decisive results cannot be obtained in the confusion and smoke of battle outside the ranges laid down in the Battle Instructions, and tat ships should be capable of coming into the shorter ranges.

4. Added to these arguments is the problem of the use of Inclination by the fast battle cruiser to provide additional security, given equal deck protection.

5. As regards speed, while it may prove necessary to accept a lower speed than 30 knots in order to provide for armour protection and offensive armament, I am much averse to this and am not convinced that we can deliberately sacrifice 2 or 3 knots without serious loss of tactical power.

6. The practice hitherto has been to provide lighter deck armour over machinery spaces than over magazines. Whether this policy should be amended or not requires examining. It is largely a question of weight.

7. Before formulating the staff requirements for a battle cruiser, apart from the present unknown factor of what the gun calibre is to be, the following major points require decision:-

(a) What is to be the decisive fighting range, assuming that a battle cruiser must be as capable as a battleship of fighting at this range?
(b) Is inclination to be taken into account, when working out thickness of armour?
(c) What is the speed to be aimed at?"

[Dave Saxton]

This is most interesting especially in light of Holland's tactics at Denmark St.

What is also interesting is what others were thinking circa the mid 30s in terms of battle ranges and IZ. North Carolina's designed IZ was 18,000 yards to 28,000 yards vs 14"/50 shell fire, or essentially 15km to 25km.

The requirements issued by the OKM for Bismarck during 1936 was an IZ of 20km to 30km ( Approx, 22,000 yards to 33,000 yards) vs 15" fire. Correct me on this but the IJN and French were thinking in longer range terms from the Germans. Littorio's inner IZ limit was 18km vs 15" though. The British are clearly the most conservative here.

The British may have been on to something because what actually happened during WWII was battles, in most cases, were fought at less than 20km. A factor for this outcome, that is often over looked, is that surface naval battles were fought more and more at night with destroyers and cruisers playing primary roles. Before 1942 only about 30% of surface naval battles were fought at night, but after 1942 90% of all surface naval battles were fought at night. By 1945 the classic Jutland style day battle with warships fighting at long range was not likely to occur.* These factors mitigated battle range to the lesser not to the greater.

With Bismarck and Scharnhorst being designed to fight at greater than 20km (22,000 yards), the scarp triangle armour scheme was a saving grace, but we find that the protection of the heavy armament a bit wanting at less than 20km battle range.

What were the British thinking in terms of belt protection at less than 20km?

* OHara

[alecsandros]

Hi Dave,
Sorry for this late reply, but I saw it late and did not have to much time.

INterestingly enough, the British battleships had the thickest single-sheet armor belt of all battleships, with the only exception of the Japanese leviathans.
That is: Nelson, 350mm belt (sloped at 18*); KGV, 380mm belt (average slope 7*); Vanguard, 350mm belt (10* slope); Lion class, 380mm belt (7* sloped).
This shows the emphasis they put on short-to-medium range combat...

However, reading through some of the papers from the 1930s, I can't help notice how much they over-rated their armor plates. One paper has the 380mm armor belt of KGV safe against 15" gunfire down to 12km.

In reality, KGV would get a very nasty shock if it went under fire from Littorio's guns (assuming they were firing properly :) )

---

As for the Bismarck class armor scheme, my impression is they tried to design it after the SK C34 guns were tested. When they saw the perforation capabilities of the new gun, they probably realized that effective protection agaisnt it at medium range was out of the question, or, anyway, required extremely heavy armor, which in turn required tonnage, which meant a huge ship.
Thus they probably thought about armoring the Bismarck's for protection outside 20km...

An interesting thing was the H-39 project.
It had, theoretically, a good level of protection against her own 16"/L52 guns, probably outside 20km range. However, against the 15"/L52 her armor scheme would work pretty neat.
This shows as the tonnage and armor thickness requried by the Bismarck's to survive gunfire from their own guns at ranges down to 16-17km: 385mm con tower, 385mm turret faces, 300mm belt with 150mm slope... 80mm weather deck with 120mm armor deck above magazines... And 63000 tons at full load...

----

Throughout the war, long range gunfire was exchanged, but only very few hits were actualy recorded...

[Dave Saxton]

However, reading through some of the papers from the 1930s, I can't help notice how much they over-rated their armor plates. One paper has the 380mm armor belt of KGV safe against 15" gunfire down to 12km.

In reality, KGV would get a very nasty shock if it went under fire from Littorio's guns (assuming they were firing properly :) )

Or they very much under rated the power of more modern guns and modern AP projectiles.

Another factor may have been an over reliance on obliqity, both in the form of slope and target angle, or combined, at these lower battle ranges. Some modern AP such as the German L/4.4 performed well at oblique angles well beyond the so called "proofing angle" implied limtations.

[slaterat]

Here's my first post on this forum so take it easy on me. As for the question of what were the British thinking reguarding the armour of their new battleships? One thing for sure is, they definitely decided to ditch the internal sloped belt concept of the Rodney/Nelson. I think as a protective scheme it involved too much sacrificial space and also allowed for the possibility of deflecting inbound shells through the bottom of the ship. Oddly enough,some of the other naval powers kept or introduced the internal sloped belt in their new designs. Obviously the British went with the concept of an external belt of the thickest, deepest , and highest quality possible within ( or slightly over) the treaty limits. Placing the magazines deep below the shell rooms also helped ensure that any possible belt penetrations would pass over the magazines. As far as I know this belt was never really tested in combat. Although the POW took a few 15 inch shells from the Bismarck I don't believe any of those struck the main belt, and in their final actions both the Bismarck and the Scharnhorst failed to score any hits. We are really left with formulas and conjectures as to how well the KGV's belt would hold up to modern 15 inch gunfire. I was always impressed with how well the Bismarcks 12 inch belt held up to the short range pounding she was given. I understand that there was very few outright belt penetrations while the turrets, barbettes and conning tower were all penetrated. Its just my conjecture that there must be something about a large thick armoured belts that absorbs and disperses shock much better than smaller structures, that is very difficult to assess.

[alecsandros]

Indeed, not much to work on.

Some elements are available though: British trials on Tirpitz plates and a British comparison of Nelson and KGV armor belt stopping power.

It woudl appear that the armor type used in KGV was a few % better than Nelson, and pretty much similar to that of the Tirpitz.
BUT there is one more aspect to consider: KGV's armor belt plates were thicker than either Nelson and Tirpitz's. So that would imply better stopping power, especialy when under attack by projectiles with a diameter of less than 380mm.

[Dave Saxton]

These are the penetration data of the German 15" gun:

Range Penetration
18km 442mm
20km 412mm
21km 392mm
22km 378mm
24km 350mm
25km 335mm
26km 320mm
28km 294mm
30km 275mm

And that's against the good stuff.

The low number of main belt penetrations on Bismarck's wreck could be due to several factors. At close range many shells could have simply flew over the hull and struck the superstructure, or hit the waves short of the target and impeded by sea water not reached the target with any energy.

At close range the impact velocity in many cases may have been too great. In other words the velocity was in the shatter zone (even capped) of the shells striking heavy armour obliquely. All shells have a shatter velocity. There is shatter velocity for the shell with a cap and without a cap. A higher than normal possiblity of shatter was a problem for British capped shells of the era. Shell Gate II. When 14" and 15"shells were pulled out of service inventory at random and tested for this they failed. Only specially built Cardinal shells passed. However, the short body 16" service shells worked during conditions in which they should have.

[Dave Saxton]

INterestingly enough, the British battleships had the thickest single-sheet armor belt of all battleships, with the only exception of the Japanese leviathans.
That is: Nelson, 350mm belt (sloped at 18*); KGV, 380mm belt (average slope 7*); Vanguard, 350mm belt (10* slope); Lion class, 380mm belt (7* sloped).
This shows the emphasis they put on short-to-medium range combat...

The protection of the armament of the British designs is also quite interesting in this regard. KGV had 324mm turret faces (albiet declined slightly) and 302mm barbet armour. The protection of main armament seems to be like Bismarck's- intended for plus 20km fighting.

The Bismarck's angled facets do come into play here though. The 180mm Wh angled facet on the crowns of the turrets was good for deflecting short and medium range fire if one goes through the calculations. To penetrate a Bismarck turret a BB caliber shell needs to hit the relatively small area front face squarely (inside of about 20km).

[alecsandros]

The protection of the armament of the British designs is also quite interesting in this regard. KGV had 324mm turret faces (albiet declined slightly) and 302mm barbet armour. The protection of main armament seems to be like Bismarck's- intended for plus 20km fighting.

INdeed, however that would not be in agreement with the heavy armor belts... Another explanation for the thin turrets and barbettes would be the likelihood that a turret hit by a BB caliber shell would be taken out of combat even if armor would not be defeated... Vanguard also had only 330mm thick faces and barbettes...

[pgollin]

.

Too many things to cover it properly, however (just from the RN perspective - I am sure much applied to other nations) ;



1: The original post covers the time when the KGVs were described variously as "Battlecruisers", "Armoured Battlecruisers" and "Battleships".



2: The most important thing is to realise that the RN believed in many things some SEEMINGLY partly contradictory ( i.e. they realised things weren't simple ) ;

a: The RN believed in fighting at a "decisive range" ( as well as fighting at any time and any place in any weather ). There is a document about this on the net. But simply, a range where straddles were often obtained and more than one hit could be expected per minute. This was why they liked armour and practiced tactics.

b: The RN FIRMLY believed in lucky hits. They realised that shells could find a single chink in an armour scheme. They believe that shells (even very heavy shells) could be deflected by quite lightweight structures, such as yard arms.

c: They believed in the ability to hit at (extreme) long range, and the fact that such a hit could be extremely effective. However, they believed that the number of hits would NOT make this an effective fighting strategy. They believed in closing to an effective range.

d: HOWEVER, they also believed in harrassing fire, that opposing ships should be fired upon as soon as possible and at least two salvos (however small) should arrive at the ships each minute. It was thought that this would have at the least a distracting effect and if any hits were obtained hopefully a demoralising one as well.



3: One should NEVER get hooked on the wargames idea of absolute figures. ;

a: Muzzle velocity - the theoretical figure was never achieved in real life even for brand new battleships because they fired proof shots and initial training rounds. Alright, each firing only reduced the m.v. by a small amount but each real life ship will have their own real life m.v. figures.

b: Armour Quality - Armour did NOT have an absolute standard quality. Some was better, some was worse than the standard. Proper penetration Tests only tested certain plates which were then never used on ships. YES, non-destructive testing were used, but one cannot be certain. Many plates were accepted above and below the standard. The RN paid contractors a premium for plates which passed by an extra percentage, meaning that certain plates on a ship would be "known" ( !!!!!!! ) to be stronger than others. This affected face hardened and homogeneous armours differently

c: Theoretical penetration figures - as it says "THEORETICAL" tests were statistical for proper "own navy" tests initial armour or shell tests would involve LOTS of test penetrations/failures to establish a THEORETICAL penetration m.v.. These tests would rely upon the experience of the testing personnel to understand the penetration and failure modes and IF any particular "success" (or failure) was due to a particularly good (or bad) shell - for the RN these shells were sent away for special examination to see what could be learnt. These results did NOT give rise to a simple theoretical penetration m.v. for a type of shell against a particular type of armour - it gave statistics which needed to be interpreted. THEN someone had to decide at what level of confidence the m.v. was to be set. Say 10% or 50% or 90% of shell would pass through at that m.v. NOT SIMPLE IS IT. I cannot find the exact criteria for the RN - but they were concerned if any tested shell failed against standard armour at above critical m.v..

IN ADDITION : different shell designs penetrated different armours differently ( ! ) - the RN realised that whilst the standard penetration formula would give an indication of penetration, it would need LOTS of tests of a different shell design to prove the critical m.v. for that design.

d: Angles and dangles - the RN ( as others) knew that the angle of inclination would affect penetration. No ship fired and had its shells hit at precisely 90-degrees to the fore-aft line. Anything could affect that angle from ordinary ship manouevring to deliberate turns to deliberately trying to keep the target ship at an angle to the enemy. This latter was part of RN tactics. In addition ships move with the sea. They pitch, roll and heave. This means that although the theoretical angle of impact might be "X", in real life this may well be different. This was examined in the RN study on armour layouts (at 5 and 10-degrees roll). In addition, waves might have an effect.

e: Accuracy - exercises versus real life engagements - the latest hilarity - one cannot just extend exercise results to real life. Yes, as with many things it gives an indication, but real life is the real test and in real life in all sorts of areas practice results were NOT reproduced.


4: Change in armour layout - this is partly covered by Raven and Roberts in "British Battleships .....", there is a larger file in the PRO. This shows many more theoretical examinations, including at various angles of heel (see "angles and dangles" above). Overall the RN saw the Internal angled belt (elongated Nelson arrangement) as per USN South Dakota and Iowa as good but that the lower belt was susceptible to penetration by large splinters, particularly the armoured cap blown through it by a shell exploding in the side protection system. They also thought the system was expensive, inefficient and very complicated to repair. By the time the KGV INITIAL designs were being looked at the decision had been made (for the heavy external system) - BUT THE PAPERS COVERING THAT SEEM TO HAVE BEEN LOST ( ?????? )


ETC ...... Etc .......... etc ........

.

[neil hilton]

Probably the best post I've ever read. Brilliant. A lot of members could learn from this when they squirt out their stats and consider them gospel. An excellent first post and welcome to the club.