Pugliese Revisited

[HogHammer]

(Note: Originally posted October 17, 2018 - Phoenix_jz)

Pugliese Revisited

 

Littorio underway in 1943

Introduction --

Designed by General Umberto Pugliese (1880-1961), the infamous cylinder-based Torpedo Defense System he developed, generally known simply as ‘Pugliese’ or the ‘Pugliese system’, has over the years since WWII attracted much attention, and generally negative. Many of the assessments, often without much of a base, have been criticized more heavily over recent years as more material and information from Italian sources has made its way into the English-speaking spheres of naval discussion (whereas previously much assessment was derived from German and British sources), and much of its capability could not be effectively judged as too much information was still unknown as to its testing. However, fortunately, that has changed quite recently, thanks to the book Aircraft Carrier Impero, by Davide F. Jabes and Stefano Sappino, the latter of which some may be familiar with as he interacted on the EU forums and ran the website Battleships & Knights (under the username ‘stefsap’) until his recent passing. Much of what the book is based on comes from the research of Stefano into the until recently unexplored archives belonging to Lino Campagnoli (1911-1975), one of the five great engineers who worked at Ansaldo from the 1930s until well after the Second World War. Within his personal archives was much information in regard to the preliminary work on the Littorio-class (particularly in regards to the hull’s shape underwater), and on the conversion of the battleship Impero to an aircraft carrier.

What is most significant to us in regards to our line of questioning is Stefano’s research in the Archives in regards to Ansaldo’s work with the Soviet Union and their tests with their version of the Pugliese system, as well as more recently discovered (not from the Campagnoli archive) information from Germany about the Kriegsmarine testing of the Impero’s hull against underwater explosions. The largest criticisms in regards to the Pugliese system are these:

• The system was vulnerable to repeated hits in the same location.    
• The system was too complicated and thus resulted in long repair times.   
• The system took up too much space that could have been used otherwise (e.g., greater ballistic protection by increasing the height of the belt below the waterline).    
• The system overall failed to adequately perform in defending the ships from torpedo attacks, as evidenced by damage taken during the war.

Thus, in this article, with all evidence available from the tests conducted against the system (and its derivatives) by the Russians and Germans, as well as looking at the effects of the wartime damage sustained by the ships equipped with this system, we shall seek to do the following;

Establish which criticisms of the system are well-founded, and fully or partially correct.
Establish which criticisms of the system are categorically unfounded and false.
Attempt to establish a realistic approximation of the strength of the system.

The Pugliese SPS --

The idea for this SPS system (Commonly known as TDS, or Torpedo Defense System in English, in Italian Sistema di Protezione da Siluro, which ironically has the same abbreviation for the USN term for their TDS – SPS, or Side Protection System) came to Pugliese when he was still a Lieutenant Colonel, in 1917. WWI had seen the loss of many battleships (dreadnought and pre-dreadnought) and armored cruisers to torpedoes and mines, and much was still up in the air as to effective defense against these underwater threats. The most common solution in that era was the use of external bulges added to the side of the warships, to put more space between the source of the explosion (the point at which the torpedo detonates, be it contact, or magnetic in later years), and the vitals of the ship. This was, albeit not terribly effective, better than nothing, but it also altered the underwater shape of the hulls of the ships that utilized it, which affected the stability and speed of the ships. Seeing as this could easily shed 1-2 knots of speed from warships, Pugliese wished to find a way around this. Thus, his SPS system was conceived. When fitted to a ship, the system would create a very little bulge on the outside of the ship, thereby not affecting stability and only causing a minor if any loss of speed. It also had the benefit of weighing less than conventional multi-layer bulkhead systems, which meant more tonnage could be used elsewhere.

The system, pictured above, worked by funneling the force of the blast on the path of least resistance, without damaging the bulkheads leading to the rest of the ship. The system was essentially two concentric cylinders. The inner, known as the absorbing cylinder, was within a larger cylinder, and the space between them was filled with liquid (potable water or fuel oil). Externally of this outer cylinder were dry cells. When a torpedo hit the system, the dry cells would immediately be destroyed, leaving the liquid spaces to take the brunt of the blast. Because liquids don’t compress like air, they would press against the cylinders. The inner cylinder was designed to fail at this point and be crushed by the pressure, absorbing most of it so that the armored holding bulkheads would take minimal force and thus not be compromised. Flooding could be minimized as only the space where the inner cylinder was would be flooded and the ruptured dry cell channels, which, connected to those on the other side of the hull via the double bottom, would allow flooding to equally distribute the weight of the shipped water. If the holding bulkhead were ruptured as well, then the same system would apply to the ship’s triple bottom, while the final bulkhead would prevent flooding in the ship’s vitals. The outer wall of the dry cells was 14-15mm of ER plating (Elevato Resistenza, or High-Resistance Steel), with the inner wall being 10mm ER. The holding bulkhead was 40mm ER, and the absorbing cylinder was made of 7mm ER. The final watertight bulkhead was 7-9mm ER. At optimal thickness (aboard the Littorio-class) amidships, the depth was about 7.22m, and the absorbing cylinder was 3.8m in diameter. Designed to defeat torpedoes with warheads of 320 kg TNT (705 lbs.), it covered the entire length of the citadel, but due to hull shape it was reduced at the ends of the citadel, so that abreast the foremost and aftmost 381mm turrets the absorbing cylinder was reduced to 2.28m (or 60% of the optimal diameter. Although not explicitly stated in any text, I extrapolate that the system depth would thus likely be 4.33m). Abreast the No.2 381mm turret, this value would be 3.04m (5.78m total depth extrapolated). Due to the complex demands of properly mounting the system, it was only possible to implement it on ships as they were built (such as the Littorio-class), or when the ship was being totally rebuilt (as on the Conte di Cavour and Caio Duilio-classes). By early 1935, however, Italian designers feared that the potential of torpedo warheads would rapidly begin to increase in power, thus potentially obsoleting the system aboard any Italian battleships by the time it came to war. This fear was not unfounded – while the torpedoes of their chief rivals, the French, had increased steadily in the interwar period from 238 kg of Picric Acid (a little over 260 kg of TNT) to 310 kg of TNT in their later torpedoes, the British were implementing surface & submarine-launched torpedoes with 340 kg TNT warheads, and with the introduction of Torpex in late 1942, this threat exploded (no pun intended), and versions of torpedoes that once contained 327 kg of TNT would being fielding 365 kg Torpex – which was equal to about 547.5 kg of TNT (1,207 lbs.)! Because of this, a series of tests were conducted against purpose-built structures “under the most realistic conditions” with various blasts up to and including a 640 kg (1,411 lbs.) TNT test. The ability of the system to absorb the blast was considered satisfactory, although lack of detail as to how it did so exactly reduces the usefulness of the test for our purposes – was ‘satisfactory’ simply that it resisted blasts well past the 320 kg intention, or because it was able to actually resist up to 640 kg? Regardless, it is likely safe to assume that the tests were conducted against a structure simulating the amidships (optimal) section of the hull.

Judging Pugliese: Obvious issues and point #1 --

As of this point, certain flaws within the system can be observed already. •    

• As the system reaches the edge of the citadel, the taper reduces the effectiveness of the system due to reduced depth, 80% of the depth abreast of No.2 381mm turret, and 60% abreast of the No.1 & 3 turrets.
• The system ends at the citadel. Because of this, it cannot protect extremities such as the bow or stern (rudders, props).
• Since the cylinder obviously cannot collapse further once it has done so, the Pugliese system cannot take more than one hit in the same spot.  
• The system is meant to deal with contact torpedoes. Magnetic torpedoes tend to go off under the hull, where only the double and triple bottoms are able to absorb the blast. This is a major weakness.

These points are obvious, and it has been used to criticize the system repeatedly. However, most of these are laughably invalid because they are standards that authors have curiously only held the Pugliese system to when comparing SPS systems. Most notably, the night of the Taranto attack is often brought up, when the rebuilt battleships Conte di Cavour and Caio Duilio were both seriously damaged by a single torpedo, and Littorio had to be grounded after taking three.

The damage suffered by the two rebuilds would seem to be the best point to criticize, as they both had to be grounded after suffering a single hit each, at both points abreast some section of the citadel, thus where the Pugliese system was meant to protect. It is worth noting from the start the systems in the rebuilds were inferior to those aboard Littorio – the maximum diameter of the absorbing cylinder was only 3.4m, just under 90% of that of Littorio’s. That being said, they also both were hit by aerial torpedoes with only 176 kg TNT warheads – just over half the strength Littorio’s was intended to defeat. 

So what happened?

Well, the torpedoes failed to hit the Pugliese system. Being magnetic, they went largely under the hull and detonated in a manner illustrated by the image below.

The impact on Cavour and Duilio, respectively

So was it a failure of the system to defeat this attack?

Simply put, it could not be fair to assume this as no TDS system placed aboard any warship in WWII was capable of defending the ship against blasts from underneath the hull.  These battleships were light, 24,000 – 29,000 ton ships with a draft less than most other modern battleships, which aided considerably in how the torpedoes were able to run almost under the hull (seeing as the same type of torpedo did not do the same to Littorio on the same night).

Damage from the torpedo hit on the Conte di Cavour

Likewise, the result of torpedo hits in the extreme bow (Littorio’s third hit on the night of Taranto, and her torpedo hit on 16 June 1942 in the same spot as the third hit at Taranto) or extreme stern (Littorio’s second hit at Taranto, and Vittorio Veneto’s torpedo hit at Cape Matapan on 28 March 1941) is unfair to use in order to critique the system as again, no battleship in the world had a TDS extending to this part of the ship. So, to suggest that this represents a deficiency with the TDS system is ludicrous in all respects.

The fact that the TDS tapers as it reaches the ends of the citadel is likewise a commonality with every torpedo defense system ever deployed at sea, and likewise is the inability to take multiple hits in the same location. Once the integrity of a given area is compromised in any TDS, it is no longer capable of resisting subsequent torpedo hits.  

Once one realizes that such critiques are against features common in all battleships, one has to question why they are so often brought against the Pugliese system as if unique faults.

Point #2: Repair Times --

Having dealt with the points above, and the first point from our original list, we shall move on to point #2 from that list. This being; “The system was too complicated and thus resulted in long repair times”.
Since WWII gives us ample examples of warships that took damage to their TDS systems, this is exactly what we shall do. According to Garzke & Duilin, “its complex shape must have made the repair of battle damage particularly difficult”, which should be easy enough to examine by comparing repair times.

This chart makes things rather simple to digest. The TDSs of battleships were not engaged frequently during WWII, but in general, the Pugliese system had the shortest repair times - the two longest times were because much more than the ship’s TDS was damaged, and involved the time taken to de-ground and raise the ships (although this chart only lists the time taken for repairs). Cavour’s repair time was indefinite because she was given low priority (Mussolini wished to repair her for prestige reasons, but the Regia Marina saw little value given its inferiority to the Caio Duilio class. Thus although the effort to repair and refit her with an even greater anti-aircraft suite was carried out, it was secondary to other concerns such as the construction of escort ships for the vital convo routes). The time taken by the Scharnhorst sisters to repair, for example, was well over twice the time Vittorio Veneto needed for a similar hit. The complexity of the design, it seems, did not hinder repair times. This again established another criticism of the Pugliese system as being categorically false. 

Point #3: Space and Optimizing for Space --

Point number three is probably the most realistic critique of the system, and is the most valid. The Pugliese system was recognized at the time in Italy it took far too much volume to work. Only large hulls could take the system, and smaller battleships could only take reduced versions, which greatly reduced its effectiveness. Alternate designs, such as the Ansaldo 5-layer system, could be implemented with similar depth and greater resistance against torpedoes, and be used to greater benefit. For example, such a benefit would be extending the main armor belt further below the waterline, improving the already impressive protection of the ship against ballistic threats. This is criticism that sticks and remains a valid point against the use of Pugliese, as it was in Italian naval circles in the 1940s.

Point #4: The actual resistance of the system --

Point No.4 (restated below) is perhaps the most complicated point, as directly relates to the efficiency of the system in wartime.

The system overall failed to adequately perform in defending the ships from torpedo attacks, as evidenced by damage taken during the war.

Thus, we shall go over each instance of the system taking damage during the war, as well as Soviet and German tests against the system, and attempt to establish some idea of its strength.

Littorio torpedoed at Taranto --

The first time any battleships utilizing this system were torpedoed was on the night of 11-12 November 1940 at the British raid on Taranto. The aircraft utilized the 18” (actually 17.7”) Mk.XII Aerial torpedo, which had a 176 kg TNT (388 lbs.) magnetic warhead, was the standard British aerial torpedo until 1943.

Conte di Cavour and Caio Duilio both fail to offer valid comparisons, as the TDS system was not involved in their loss, and no battleship of their displacement would offer an effective defense in such a situation against torpedoes.

The first hit was sustained by Littorio at 23:15 at frames 162-163, which is directly abreast of the fore 381mm turrets, and within the area protected by the TDS. At this point in the hull, the absorbing cylinder would be just about two and two-thirds of a meter in diameter or about 70% of the maximum value. This first torpedo blasted at 10x7.5m breech into the dry cells of the TDS but failed to breach the 40mm armored bulkhead, the system working almost perfectly. That being said, there was minor flooding, due to a 2.8cm crack at the bottom of the armored bulkhead, and another minor one in the 7-9mm longitudinal watertight bulkhead, causing some flooding in the No.1 turret magazine, likely due to defective seams resulting from the welding. Upon analysis by Admiral Bergamini, who was the inspector for the damaged ships, and also in charge of the fitting-out of the battleship Impero, concluded that several issues faced by the ship’s resistance to torpedo damage and flooding that night (mostly directed to the third hit) resulted from a rushed and thus lower-quality fitting-out compared to her sister Vittorio Veneto. Thus, in spite of the minor defect, the system worked.

Giulio Cesare bombed in Naples --

The next time the system was tested was in January of 1941 when a British air raid on Naples resulted in a 250kg bomb detonating about 4 meters from the hull of the rebuilt Cavour-class battleship Giulio Cesare. The explosion, roughly about 130 kg of TNT, was abreast the forward engine room. Although the outer dry cells were destroyed, the armored bulkhead had no damage and the ship sustained no internal flooding, with the absorbing cylinder in the location of the blast being crushed as intended. Repairs only took 12 days. It is worth noting that the system was inferior to that of Littorio’s, with 89% of the diameter. However, this is more than the section of hull that took the Mk.XII on the night of 11 November 1940 (70 %), and the blast was lesser, no more than 130 kg of TNT. Nevertheless, it showed that the system did in fact work in theory as predicted. It is also the only time the Pugliese system was engaged on one of the rebuilt battleships.

The result of the bomb detonation abreast "Cesare"

Vittorio Veneto torpedoed by Urge --

It was not until December 1941 that any ships would again take damage to the TDS, and this was the Vittorio Veneto, during Operation M.41, torpedoed by the submarine Urge. The impact was with a Mk.VIII torpedoes fitted with a 21” 340 kg TNT (750 lbs.) warhead, striking the port side abreast of the No.3 turret. As you will recall from earlier in the article, at this location the cylinder diameter was only 2.28m (60%). In this example, the system was overwhelmed and failed, both the armored bulkhead and the longitudinal watertight bulkhead. The ship immediately took on a 3.5º list as 2,700 tons of water flooded into the ship, but the balancing channels resulted in this being rapidly corrected to only 1º (with the aid of 300 tons of counterflooding). The ship’s damage control systems worked effectively, not only with regards to the list being corrected but also the venting of toxic gasses and the effectiveness of the high-capacity pumps in combating the spreading of flooding. Thus, the machinery remained operational with no direct damage, but the aft 381mm magazine was flooded. The propulsion machinery was able to make full normal power, so Vittorio Veneto rejoined formation, catching up to her sister Littorio, and returned to port at 23.5 knots without further concern. Repairs only took two months. At the end of the day, while solid construction and effective damage control had prevented any serious threat to the ship’s safety (although it made the aft main battery turret unable), the TDS had failed the ship allowing such a breech and flooding to occur.

"Vittorio Venento" making good towards Taranto, in spite of a torpedo hit

Littorio damaged by a PC 1400X "Fritz X" --

The last time Pugliese would be tested in combat would be on the fateful day of 9 December 1943, when the battleship Roma was lost to PC 1400 X radio-guided glide bombs (The “Fritz X”). In the same attack, the battleship Italia (the ex-Littorio) would also receive damage. Ironically, the relevant location was in much the same spot as the torpedo that stuck at Taranto – between the fore turrets, starboard side. The bomb had actually struck the upper deck (36mm on 9mm laminate), continued down to the ‘main’ deck (12mm), and then passed out through the 70mm plating that made up the upper belt. It then continued on into the water about 6 meters from the hull before exploding. Its warhead was 320 kg TNT (705 lbs.) and had much of the same effect as a torpedo. As mentioned previously, the absorbing cylinder was at about 70% diameter in this location. In this case, a 7.5x6m breech was made in the dry cells, and crushed two of the cylinders. However, the armored bulkhead suffered no damage and neither did the watertight longitudinal bulkhead. 1,066 tons of water filled the TDS spaces causing a 3º list, but with the automatic balancing channels and the pumping of 180 tons of water into bulges, this was corrected. The ship continued with no serious issues, unimpaired, and although never repaired, the estimated time to repair was 1 & ½ months.

Thus ends the combat record of the Pugliese system.

Kreigsmarine tests of Impero’s hull --

The next time it would become relevant was in July of 1944 when the Kriegsmarine began conducting tests on the hull of Impero.

The first two tests had the internal cells of the system dry, but they were not affected by the tests, as these were conducted in the forward section of the ship. However, the third test, with the system fully operational, was conducted abreast the forward machinery spaces (where the system was fully implemented). A 330 kg charge of S1, or 511.5 kg TNT (1,128 lbs.), was placed directly against the hull and detonated. The majority of the blast was absorbed by the system, and the longitudinal bulkhead remained undamaged, although the armored bulkhead seems to have been breached (the text does not explicitly state so) with some flooding beyond it, but this was taken care of by the balance ducts (implication seems to be that of the triple bottom, which is where I derive the assumption of the armored bulkhead being breached).

The Kriegsmarine was impressed with these tests, as tests with 300 kg S1, or 465 kg of TNT (1,025 lbs.), against the systems of the Deutschland-class cruisers, Scharnhorst-class battleships, and Bismarck-class battleships, had all overwhelmed the entirety of the systems. It is perhaps worth noting that USN Post-War technical missions rated the TDS of the Bismarck-class was at 900 lbs. TNT, or 408 kg (The document actually states ‘900 kg’, but this is obviously an error, as that would mean the TDS could resist almost 2000 lbs. of TNT).

A final test was conducted with three charges of 300 kg S3 (459 kg TNT each, or 1377 kg/3,035 lbs. TNT) at 7 meters depth and 17 meters off the port side of the ship. In this case, the system was breached, resulting in flooding between frames 123 and 129.

Ansaldo projects for the USSR & Soviet testing of Pugliese --

The last examples we will look at don’t quite match up in terms of the path we’ve been taking (linear through time). We’re going to rewind the clock, back before the war started. As is well known, the Italian companies and the Soviet Union had substantial cooperation prior to WWII, and essentially every modern design produced in the USSR evolved from Italian designs, modified to suit Soviet preference. This was no different in regards to battleships, and Ansaldo sold a derivative of the 406mm battleship project (the 1935 version specifically) to the Soviet Union as UP.41. Although commonly referred to as a larger, better armed, and armored version of the Littorio-class, it’s not clear how true that was given the armor scheme appears to be largely inferior, and it also utilized a three-layer Ansaldo TDS rather than the Pugliese system. However, through a special agreement information about a system similar to Pugliese was shared, and the Soviets were ultimately able to come by the full information about the TDS (espionage?).

Although the Soviets did not choose UP.41 for their next class of battleship, it did heavily influence the resulting design, Projekt 23. When examining different systems for use, they decided to test seven systems; that of UP.41, the Pugliese system as on Littorio, a 7-layer system from the American West Virginia-class battleships, the original Pugliese system fitted to two Italian tankers, the TDS of the British battlecruiser Hood, and two native Soviet designs. The tests found the Pugliese (Littorio) and the 7-layer West Virginia system to be the best systems, but due to the greater difficulty of building the Pugliese system for Soviet industry, it was proposed to use the American system instead. Further tests were conducted in October of 1938, where 400 kg and 500 kg blasts (against the American and Pugliese systems respectively) left the inner bulkheads of the systems undamaged. Ultimately the Soviets decided to implement the Pugliese system, albeit with some modifications.

In August 1942, due to the fall of Sevastopol to Axis armies, Ansaldo had the opportunity to examine the hull of the incomplete Sovetskaya Ukraina, and her modified TDS. The Ansaldo technicians determined the system was inferior due to a number of important reasons.

Due to the continuous welding techniques needed for the armored bulkhead being beyond Soviet capabilities at the time, Pr.23 used welding points and heat riveting, which compromised the strength of the system.  
Based on their own testing, the Soviets thinned this bulkhead to 30mm, and 35mm where the system was thickest (whereas in Italian practice it was 40mm).    
The design did not incorporate a triple bottom, instead only relying on a double bottom.
Despite these shortcomings, the Soviets seemed confident in their version of the system being able to do the same job, and thus this made up the majority of the torpedo defense system of the Sovetsky Soyuz-class (Pr.23) battleships.

Concluding resistance --

In regards to its ability to resist damage, we have an easy list of examples of the system’s resistance to damage via tests and combat records:

As one can see above, the taper of the system greatly affected its capability. When the system was fully implemented, it worked incredibly well, resisting blasts in excess of 500 kg. However, abreast the No.2 turret the system’s diameter was reduced to 80%, and abreast the No.1 & No.3 turret it was only 60%.

A rough graphic of the taper

This plainly reflected in the performance of the system during the war. When a PC 1400 X detonated off Littorio’s portside with the force of 320 kg of TNT, the system was able to resist it perfectly. The diameter was only 70%. When the same result was delivered by a 176 kg warhead from a Mk.XII aerial torpedo, the system also resisted it. However, when a Mk.VIII torpedo with a 340 kg TNT warhead detonated abreast the No.3 turret where the system was only 60% capacity, the system failed, which put the No.3 turret out of action as a result. Of course, when a 1377 kg of TNT went off against her side, the system failed – but nothing would resist that.

Unfortunately, we lack much in the way of examples of modern warships to compare it to, as there aren’t many that took torpedoes and, well… survived. Prince of Wales, Bismarck– We’re looking at you. Perhaps two of the few examples that are usable are Scharnhorstand North Carolina– since both suffered individual hits at one point in their life.

Scharnhorst was struck by a Mk.VIII torpedo (340 kg TNT) abreast the No.3 turret (launched by Acasta during the sinking of the Glorious). Her system, 4.5 meters in depth amidships, was designed to resist 250 kg of TNT.  Abreast the No.3 turret, it thinned to only 3 meters (66%), where it was only considered capable of stopping 200 kg of TNT – and was totally overwhelmed on impact. The impact was similar to the hit of Urge on Vittorio Veneto. The damage was much more extensive on Scharnhorst, as although the flooding of the aft main magazines (taking the No.3 turret out of action) occurred on both ships, elsewhere was not the case. Vittorio Veneto took more overall flooding (2700 vs. 2,500 tons), but it rapidly stemmed and did not spread elsewhere. The engines remained undamaged and the ship was able to continue on normally at a cruising speed of 23.5 knots. The German battleship, however, suffered much more extensive damage and flooding, which disabled both the starboard and center turbines, not to mention destroying the starboard shaft. Relying on the port turbine, the Scharnhorst limped back to port unable to make more than 20 knots. It is perhaps also worth noting the initial impacts gave Vittorio Veneto a 3.5º list and she was down 2.2 meters to the stern, but counterflooding of 300 tons corrected the list to 1º. Scharnhorst in contrast took a 5º list and was down 3 meters by the stern. Vittorio Veneto took 2 months to repair. Scharnhorst, 5 months.

North Carolina took one of I-19’s 533mm Type 95 torpedoes in a spread that famously sunk the carrier Wasp and the destroyer O’Brien. The 405 kg Type 97 warhead (433 kg TNT) detonated abreast of the No. I turret, where the depth of the system was reduced to 77% of its maximum strength (~4.34m vs. 5.64m).

The torpedo detonated 6 meters below the waterline and blew a 9.75x5.5m hole in the side of the ship, ripping past the four torpedo defense bulkheads and causing a breach in the last bulkhead, a section of class B armor that tapered from 89mm down to 53mm in place of the usual bulkhead elsewhere in the system. A flash was reported in the fore magazines, risking a magazine detonation, and the ship immediately took on a 5.6º list to port. Fortunately, due to the fact the liquid spaces in the protective systems were largely full, only 970 tons of flooding was taken on, with an additional 480 tons of water taken on as counterflooding, removing the list (but not trim), and bringing the total tonnage taken on to 1,450 tons. She was able to continue on, her maximum speed now limited to 25 knots, but not substantially worse for wear despite the flooding into her magazines.

This is far from perfectly analogous to any hit taken by the Littorio’s, but it best compares to the starboard-side detonations taken between the No.1 & No.2 turrets, where her TDS was only at 70% depth – and resisted explosions of both 176 kg and 320 kg TNT, the latter flawlessly.

No direct comparison can be made from these, as the warheads were of significantly different strength – the hit North Carolina sustained was a third again as powerful as those Littorio sustained. However, it is at least worth noting that Littorio’s system strength was reduced more so than North Carolina’s in this area (70% vs. 77%), and also lacked any additions to increase resistance despite this – namely, the Class B armor plate dropped around North Carolina’s fore magazines as additional protection. That being said, it should also be noted that the fact that Littorio’s SPS depth was reduced further than North Carolina’s despite the spot in question being behind the No.1 turret rather than abreast it (as on the American battleship) is not a good thing for Littorio – it does show that the system depth is further reduced in extremities than compared to other ships. In fact, Littorio’s system would’ve only been 60% diameter at the same location. And, as we've shown before - 60% diameter was unable to resist 340 kg of TNT. The same would be true of a 433 kg TNT blast.

Thus, in regards to the system strength, it is abundantly clear that it is very strong, with the ability to resist over 500 kg of TNT (1100 lb.). This puts it up as one of the strongest systems of the war – to compare with the other ‘final’ Axis battleships, US technical missions post-war rated Bismarck’s system at 408 kg TNT, and Yamato at 236 kg of TNT. USN Fast Battleships were all rated at 317.5 kg TNT (700 lb.), but on North Carolina, at the very least it proved to be able to resist much more than that – falling just short of resisting 433 kg TNT at 77% depth, although it should be noted the addition of the Class B armor plate greatly helped her ability to resist it.

The reduction towards the extremity hurts the strength of the system significantly – as evidenced by failure to resist a 340 kg TNT blast at 60% diameter. So, should the taper be considered a great disadvantage of the system compared to others? As mentioned, North Carolina’s taper was far less.

Compiling a list of tapers yields this:

Thus, the average taper lines up with Littorio’s almost perfectly – 60%. Thus, the taper of the Pugliese system on this ship, while not good (merely average), is far from an Achilles heel of the ship.

In fact, if we establish a linear relationship between the absorbing cylinder diameter and the blast resistance, it explains these hits perfectly. 100% resisted 500 kg. 70% resisted 320 kg, and 500 * .7 = 350 kg. 60% failed against 340 kg, and 500 * .6 = 300 kg. This produces a graph as such:

Of course, this graph should be taken with a major grain of salt – we simply lack enough data points to determine how accurate such a line could be – it works, but it’s vague. We lack any data on hits abreast No.2 turret (or forward of No.3), where this system is 80% diameter, and likewise, we only have a point of value for 60% diameter. For all we know, this could be a ‘critical diameter’ where the system will fail against anything, but any greater diameter will resist it. It sounds ridiculous – but, again, that also fits the available data.

At the very least, we do know the system for the most part is strong enough to resist the blasts it was designed to, for the most part. Able to absorb the planned 320 kg TNT blasts at 70% diameter, just aft (or fore) of the turrets located at the extremes of the citadel, the vast majority of the system does meet the design requirement – and indeed for its greatest portion (abreast the machinery) it proved to be able to absorb blasts 60% greater than what the system was designed for, no small feat. Whether the very ends of the protective system meet the requirement, however, is unknown.

Some last notes on misconceptions --

This last section I’m going to dedicate specifically to the misconceptions shared by Garzke & Dulin in their chapter on the Littorio class. One of their prime points of criticism is “the susceptibility of the system to failure under heavy loadings from non-contact detonations, due to the inadequacy of the riveted joint joining the protective system to the bottom structure of the hull girder”, which they credit the loss of the Roma too. This however is largely impossible, as the first PC 1400 X that struck Roma detonated under the hull and had no interaction with the system - flooding came up through the bottom, not through the sides of the ship. The second hit detonated within the hull and set of the magazines, and had nothing to do with the Pugliese system either.

Likewise, the system did not make use of rivets, and it is not clear why the authors believed this was the case. It is perhaps possible they based the consideration on the Soviet copy of the system, which did make use of riveting.

Conclusion --

So finally we must come to a conclusion about Pugliese in light of reviewing its performance and past assessments. To put it simply, I am largely in agreement with the opinions Stefano has shared both in the book and in posts on the forums & his website. Many of the classic criticisms of the system seem to be unfounded and compounded by incorrect information about the system and its wartime performance. Likewise, unusual standards applied to the system have also factored into these critiques, including the failure to protect extremities and the loss of system effectiveness at citadel extremities due to taper. Even when damaged, repair times were not above average, and that’s despite the fact that such time was usually also taken to improve internal systems and damage control capabilities.

Thus; criticisms expressed like this from navweaps.com, from Joseph Czarnecki’s page on TDS systems:

…Do not necessarily hold up.

Myth-busting, and the strengths of the System --

For example, both Conte di Cavour and Caio Duilio are cited as examples of the system failing when they were not involved, and nor could any contemporary TDS system. Only one of Littorio’s three hits was against the TDS, and this had little effect on her… then of the examples cited at sea, only one actually hit the TDS, the rest being in the extremities of the ships. Of the examples cited above there are eight torpedo hits – only two actually interacted with the TDS and thus can be used to judge it.

Long repair times also seem to be an excessive criticism, given repair times were not above average for other battleships taking torpedo hits to their torpedo belt. In fact, they were more rapid compared to many of their contemporaries.

To be perfectly blunt - I lack any professional education in metallurgy and hydrodynamics. Thus, I cannot contest such an assertion, from a physics point of view, that the blast would ignore the absorbing cylinder and instead concentrate its force on the 40mm ER bulkhead. That being said, what I can say is that such an assertion was largely disproven in practice, given the multiple successful tests of the system in combat and in (literal) tests. There is only one actual example of the system outright failing in combat, at the point where the system is at its absolute weakest.

Likewise, if such a defect in the very theory the system was predicated on existed, then it would have most surely revealed itself in the 1935 tests which tested the Pugliese cylinders with TNT charges of up to 640 kg.

In practice, the ‘meat’ of the system, that is, the portion abreast of the machinery, which is the thickest on every TDS design, proved to be one of the strongest systems to be fielded on any battleship of the Second World War. Able to resist blasts of up to at least 512 kg, this puts her on the same level as systems such as those used by the North Carolina-class battleships, who have the reputation of perhaps the strongest SPS system fitted to any American battleship, and by extension (given the usually excellent quality of American SPS), to any battleship ever constructed. It is clearly stronger than those of her Axis competitors, but against a few others it is not so clear.

These few others are:

• King George V – Only Prince of Wales was torpedoed, but she was swarmed and her loss was due to a tragically unlucky hit, perhaps the unluckiest in the entirety of naval warfare. A Japanese aerial torpedo with a 150 kg Type 97 (160.5 kg TNT) hit her directly where one of her outboard shafts met the hull, breaking it and causing the shaft to literally gut the ship, ripping apart the watertight bulkheads in the interior and allowing massive flooding directly into the engine room. Given the TDS of the King George V-class battleships was designed to resist 1,000 lb. of TNT (454 kg), it is almost assured that the system resisted the torpedo hits along it. However, no system could save a ship from such an unfortunate hit. That being said, we don’t have any real data on the resistance of the system so it makes it difficult to judge. It was overall one of the shallowest systems of any modern battleship, with a maximum depth of just 4.0 meters.
• Dunkerque & Richelieu – Despite the latter being much larger, their TDS was practically identical. Paradoxically, it was actually half a meter deeper on the Dunkerque class (7.5 m vs. 7.0 m). On the aforementioned class, it was designed to defeat a 300 kg TNT blast. However, I lack any data on French tests of the system, and likewise, they were not tested in combat.
• South Dakota & Iowa – These battleships use a largely identical system, designed to resist up to 700 lb. of TNT (317.5 kg), as was North Carolina’s.  However, it differed due to the decision to use a more inclined belt and a lower belt to protect against diving shells. However, because of this, it has generally been judged as inferior to North Carolina’s excellent system (essentially, the Americans made a trade – ballistic protection in favor of torpedo protection). That being said, it is still unknown as to what the real effectiveness of the system is, due to the fact the last Iowa-class battleships (Iowa and Wisconsin) were stuck from the naval register only in 2006, twelve years prior to this being written, and the data is still classified. It is worth noting that Iowa’s system is slightly improved from South Dakota’s; most notably in the fact the joint between the lower belt and the triple bottom is stronger (and the lower belt is also thicker in this location on Iowa compared to South Dakota).

So, if we’ve gone over all the flaws that didn’t exist within the system despite their repetition for so long, as well as establishing how strong the system was… let’s conclude on their weaknesses and a final assessment.

First of all – the taper. Without a doubt, the taper greatly affected the torpedo resistance of the Littorio-class, and although the torpedo it failed against was 20 kg stronger of a yield than what the system was designed to counter, as evidenced by other blasts this was far less than what the system could resist in practice. Although earlier we did establish that this was hardly unique – in fact, the taper is ‘just average’ compared to other battleships – that is hardly an excuse. While better than the taper of the other European battleships, and of course the elongated Iowa, it is still a massive reduction that is not (nearly) as present on the excellent system used by North Carolina, and even King George V, while hardly boasting a deep system, is at least much more consistent than that of Littorio. This also leads to my next point.

The true prime flaw of the Pugliese system --

At the end of the day, for all its strengths, the Pugliese system is very inefficient. The system takes up an enormous volume, and I am in total agreement with the final paragraph of Czarnecki’s statement about the Pugliese system. The system ate up a huge volume on the ship, which was space and weight that could’ve gone to more productive use.  The great height of the cylinder removed any possibility of a lower belt, which reduced the vertical protection of the ship (which was otherwise perhaps the strongest of any ship of WWII). It also reduced the internal volume available for what goes in the citadel itself – namely, greater ammunition storage and more powerful machinery (which was one of the early sacrifices of the design).     

Ultimately, within Italy other systems did exist that were more conventionally based, that would not only take up less volume and more easily integrate with the ballistic protection of the warship, but were also at the end of the day, an all-round stronger system (namely, the Ansaldo 5-layer system).     

The final assessment --

In the end, I do agree with Czarnecki’s last line, although certainly not in the way he intended. The Pugliese system was innovative, and was overall effective, but not for what it cost the ship. It was not so much a step backward, but a step sideways – a more effective design than what preceded it, but not a replacement for more conventional methods, which on the same depth could produce superior results.

That being said, compared to contemporary systems it performed its job well and successfully, and was stronger than most other systems fielded. At the end of the day, had a stronger system been fitted it would not have made any difference in the employment of the Italian battleships, and nor would it have made them any more effective (assuming benefits brought from reduced TDS volume). No system could save the rebuilds at Taranto, and no system could prevent the damage from the hits sustained outside of the citadel – which are the ones that had the greatest effect (Littorio at Taranto, and Vittorio Veneto off of Gavdos). What truly hindered the employment of the Italian battleships was threefold; lack of fuel oil in 1942 & 1943, the lack of effective air cover for most of the war from either the Regia Aeronautica or the Luftwaffe (both in providing fighter cover, and effective scouting), and a lack of radar to effectively employ the battleships at night (where aircraft were less of a threat, not to mention reducing the need for aircraft as scouts in day or night). The combination of these factors limited the ability of the Italian battleships to make contact with the enemy, accurately judge their strength, sustain contact, and engage in equal terms in poor visibility conditions – and eventually, limiting their ability to sortie in the first place.

Sources -- 

The Littorio Class: Italy's Last and Largest Battleships 1937 - 1948 - Erminio Bagnasco & Augusto de Toro

Aircraft Carrier Impero - Davide F. Jabes & Stefano Sappino

Axis & Neutral battleships in WWII - William H Garzke, jr & Robert O. Duilin, jr

French Battleships 1922 - 1956 - John Jordan & Robert Dumas

Naval Weapons of World War Two - John Campbell

Battleships & Knights - Stefano Sappino

"Torpedo Defense Systems of WWII" (navweaps.com) - Joseph Czarnecki

"Naval Weapons of the World (torpedoes subsection)" (navweaps.com) - Tony DiGiulian

 

[Wolfswetpaws]

Nice "food for thought" to go with my breakfast & coffee.  Thanks for sharing.  🙂 

[Talleyrand]

This is excelent work.