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The_first_harbinger

"Why can't I citadel Henri's board side?" A detailed analysis of the spaced armor mechanics in World of warships

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     To those that have played world of warships for quite a while, engaging enemies of all shapes and sizes, including the French cruisers, the following might some familiar to you.

"A careless Henri IV has come into view, barely angled. I think she's close enough, I have sufficient penetration. Ohh, I am so going to make him MINE!"

The shells fly true, sticking dead center in the careless cruiser. But, Merdé, there's no citadel, only penetrations, and what's more, it barely does any damage, around 2k~3k!

Tchevo Blyat??!  Does the Henri use black holes for armor?

             To explain what is happening, we need to understand the key mechanics that acts as the armor-piercing shells' principle. 

Let's first examine the armor layout of the French cruiser. (Diagram not drawn to scale)

1816484203_ScreenShot2018-11-28at19_25_41.thumb.png.40821cbd2f3c79207fb9888779ec96b3.png

Alright, moving on to the Armour piercing mechanics. For a shell to penetrate a section of a ship, the mechanics have different priorities.

Spoiler

1. Overmatch. Pretty self-explanatory, and it doesn't matter for this discussion.

2. Bounce check. For normal AP shells, the bouncing angles are between 45-60 degrees. For shells that strikes the armor at an incline more than 60 degrees from the perpendicular line against the armor surface, the shells are guaranteed to bounce. Likewise, for shells that strikes the armor less than 45 degrees, the shells are guaranteed to penetrate, anything in between are under the mercy of RNGesus. (Note: The normalization mechanics only cames into effect after the shell has passed the shell bounce check, and applies only to penetration. In the game, it doesn't really change the trajectory of the shells, and it only works in penetration calculations)(Note 2: As we should all know, some ships have modified angles, like 60-67 degrees for tier 8,9,10 USN heavy cruisers and the Hood, 60-75 for British cruisers, etc. etc.)

3. Penetration check. This is pretty straightforward. Your shell loses penetration over distance due to multiple factors, and if you have enough penetration to overcome the thickness of the armor, after normalization and shell bounce check, the shell goes through. If not, well, idi nahui!

4. Shell fuse prime check. For a shell to began arming the fuse, it needs to penetrate at least 1/6th millimeters of  Equivalent Armor for the shell fuse to prime. The word "Equivalent Armor" is important. For example, Yamato's AP shell requires 77mm of armor to prime, and a Khabarovsk's belt is 50mm. Theoretically, every shell that struck the ship should over-penetrate, but if you angle, therefore increasing the relative equivalent armor past 77mm, the shell will prime, and your boat is pizdec. The equivalent armor is calculated by     Armour Equivalent = COS( Vertical shell drop angle + Armour angling - normalization)

5. Shell fuse time and shell travel time. After penetrating an armor belt and with the fuse primed, the shell began its deadly timer and continues on its merry way into the enemy ship. After penetrating an armor, the shell does not lose speed, only penetration. For example, if a shell has 300mm of penetration at the point of impact, and it struck a 50mm armor belt, the shell will have 250mm of penetration as it continues inside the ship. The Overmatch, Bounce, and Penetration check will activate EVERY TIME the shell meets a piece of armor. There are two ways that your shell can overpenetrate. Either the caliber of the shell is too great, and the shell never met enough armor to prime the shell through the entire ship, or the shell is too fast, and the enemy ship is too narrow, that by the time the shell fuse run out, the shell has already left the enemy ship. Again, some special cases have special treatments, all British cruisers have a shell prime threshold of only 12mms.  (Note: On the rumors of "Citadel overpenetration" it isn't true. If your shell failed to prime even after penetrating the entire citadel of the enemy ship, the shell will over penetrate through the citadel and do nothing special) 

      Okay, back on topic. Why does the Henri IV eat your armor-piercing shells and receive little damage?

The answer lies in the empty space between the main belt and the citadel bulkhead. The 140mm main belt is enough to prime any shell in the game, which means for the shell to fail to citadel the Henri IV, the shell is either too slow, have too short of a fuse, or doesn't have enough penetration to penetrate the citadel bulkhead. The empty space between the main belt and the citadel bulkhead have extremely low modular health, meaning it can saturate very easily, and should a shell detonate in this section, the ship takes minimal damage.

To test this, we must first know the shell fuses that are present in World of Warships

1. Small caliber destroyer guns with a caliber of 130mm and below have a fuse delay of 0.01 seconds.

2. 130mm-155mm light cruiser guns have a fuse delay of 0.025 seconds.

3. 180mm-460mm heavy cruiser and battleship guns have a fuse delay of 0.033 seconds.

(Again, special cases. British battleships (excluding Warspite and Vanguard) have a fuse time of 0.015 seconds, while British cruisers (excluding payfast) not only have a fuse time of 0.005 seconds but also have an extremely sensitive fuse that primes the shell after penetrating only 12mms of armor.)   

      Let's prove it.

Spoiler

Take, HMS Neptune, for example.

923927855_ScreenShot2018-11-28at20_20_59.thumb.png.bb65d777c66b51eb7a3b2c4c68acebf5.png

Which means

279408705_ScreenShot2018-11-28at20_25_08.png.ae584cb268964d7ba898d7a6597430de.png

This can and will happen. Penetration isn't an issue, at this range, Neptune can citadel Des memes and Moskau just fine. Which means it's time to run the shell through our mechanics. 

Neptune's shells exit the barrel at a velocity of 768 m/s, barely loses and penetration or velocity at such close range, after penetrating the 19mm torpedo bulge, the extremely autistic and hypersensitive British shell primes, and continues to travel toward the citadel for 0.005 seconds. The shell can travel around 3.75 meters during this period, which is not enough for the shell to reach the citadel.

 

So, let's crank up the steam, and see if we find the sweet spot between citadels and disappointment.

Spoiler

Let's take out my personal favorite, the Graf Spee, striking the Henri IV at a range of 10.6km

1542942037_ScreenShot2018-11-28at20_38_00.thumb.png.aafa3caf386b2b9165f103b873da9341.png

The Graf Spee have a short-fused shell. The shell will detonate after 0.01 seconds after priming the fuse. The shell can travel slightly less than 5.11meters after penetrating the main armor belt of the Henri IV. Is it enough? Well, the answer is quite mixed. Sometimes citadels are scored, sometimes the shells caused zero to no damage. This is because of the 20 degrees incline of Henri's main belt, the higher the shell lands above the waterline, the bigger the distance the shell have to cover in the empty space.

 

      So, what does this all mean?

This means that any shell that ran out of fuse time and detonates in the Henri's spaced armor will be absorbed with minimal damage caused. And not just because the shell ran out of fuse time. We can expand on this mechanics. 

Remember the shell bounce mechanics? It applies every time a shell strikes a piece of armor.

So, let's suggest if a Montana's 406mm superheavy shell stuck a Henri 10km away, at 60 degrees, and the Montana is lucky enough to pass the shell bounce check and go through the main belt. The shell has a velocity of 564m/s at this range, with a 0.33 second fuse time, the shell can travel around 18.6 meters before detonating, way further than the 10 meters effective empty space. Then why can the shell still be absorbed?

The answer lies in the citadel bulkhead. Again, the shell bounce mechanics applies every time a shell meets a hard place. Despite passing the shell bounce check at the main belt, the 45mm citadel bulkhead is too thick to be overmatched, and the shell bounce mechanics is applied again. If the RNG dictates that the shell bounced, the shell will detonate inside the empty space between the main belt and the citadel, and cause minimal damage.

 

Another infamous example is the British BB HE shells. We can consider the HE shell as an AP shell that doesn't bounce, have perfect normalization, have a fuse that primes after meeting any armor, with an absolute 0 fuse time. Let's take Conqueror with 419mm guns (because 457mm guns don't matter and we all know it) against the Emile Bertin, the shell will easily penetrate the belt of the unarmoured cruiser and detonate immediately. Despite having enormous penetration, the shell will never touch the citadel and cause minimal damage. Try this for yourself, take a British BB to the training rooms, aim at an Emile Bertin at point-blank range dead at the waterline, it watch it cause at most 3000 damage.

      Conclusion

French cruisers are broken plz nerf The unique armor layout gives the French cruisers unique advantages, that especially rewards angling while tolerating more mistakes against certain ships. If you find yourself in a British cruiser or a destroyer, shooting at a Henri, it might not be the best idea to aim for the main belt. Try to aim for the higher auxiliary hull, where you can score reliable 1/3 or 1/6 damage depending on the point of impact.

Edited by The_first_harbinger
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In addition, shell's velocity after impact is likely determined by this equation: 

v_2 = v_1 * (1-exp((d-p)/d))

p: penetration d: layer thickness v: velocity before and after

Source: 

I do also have a program that can calculate post pen detonation distance after penetrating single plates of armor though it does not yet work with multiple plates - so if anyone wants some data from that I am happy to provide it. 

Edited by 901234

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