Detonation Mechanics with Sub_Octavian

After making a little post about detonations (which you can read here!), I was approached by Sub_Octavian from Wargaming who volunteered to answer some questions I had about detonations.  You can imagine the excitable, ear-breaking, high pitched sounds that I made at that moment (my corgi sang along). The jumbled, confused battery of questions I inundated him with doesn’t make for very comfortable reading, so I shall paraphrase him and quote directly where applicable into a more comfortable narrative.

You said it, Queen Cordelia!
What We Knew…
Some aspects about magazines were already well known and documented on the World of Warships wiki:  Magazines are a module and have special rules for how they take damage. They have their own internal hit points completely separate from the ship’s hit points.  Attacks which successfully hit a module depletes this hit point total.  Each time a module takes damage, there’s a chance it will be temporarily disabled, though these critical hits are not universal across all module types.  Main Battery, Torpedoes, Engines and Steering Gears all can take these critical hits while AA guns and Secondaries cannot — these latter mounts existing in a binary state of “fine” and “destroyed”.  Using your Damage Control Party will restore these temporarily disabled modules back to working order immediately, otherwise there’s a short delay before they repair themselves.  Once a module’s hit points are fully depleted, it is destroyed.  Your Engines and Steering Gears cannot be destroyed, but repeated hits can temporarily disable them again.  There is no recovering a destroyed module.
Magazines are a module very similar to Engines and Steering Gears.  Depleting their hit points does not cause a detonation — instead, it’s the critical hit mechanic which sets these off.  Each attack which successfully damages the magazine has a chance to detonate the magazine.  The more damage a magazine takes, the higher the chance each attack will cause a detonation, reaching an upper maximum when the magazine’s hit points run out.  This upper maximum value never reaches 100% but we were never told what it was…
What We Didn’t Know…
All ships have the same chance to be detonated when hit in a magazine that has lost all of its hit points.  This value is 10%.  I say again, there’s a 1 in 10 chance of setting off a detonation upon a fully depleted magazine with every hit that strikes it.  This value can be modified by the use of signals and modules.  These bonuses are multiplicative.  For example:
Fully Depleted Magazine
India X-Ray (5% increased detonation)
Magazine Modification 1 (70% reduced detonation chance)

0.1 * 1.05 * 0.3

3.15% detonation chance per hit to magazine
The Juliet Charlie signal drops the chance of detonations down to zero, no matter what.
This chance of detonation is universal across all ships and all tiers.  To quote Sub_Octavian: “… the proportion is universal across all ships. Yamato fully destroyed magazine has a 10% detonation chance when being damaged. Katori fully destroyed magazine also has 10% chance.”   This value scales equally too — no ship has a greater chance of detonating per successful hit to their magazines.  A Fuso that takes damage which reduces her magazine’s hit points to 50% has the same chance of detonating as a Fubuki that gets her magazine’s hit points reduced to 50%.  But herein lies the catch:
  1. Some magazines are harder to damage than others.
  2. Some magazines have more hit points than others.
This helps explain why some ships just seem to blow up more, or why certain ships seem more vulnerable to different kinds of attacks.
Magazine Resilience
There are four different attacks that can do damage to a Magazine:  AP Shells, HE Shells, Bomb Hits and Torpedo strikes.  Ramming, flooding, fires and harsh language do not affect magazines (even though it feels like they should).  Successfully hitting a magazine with each weapon takes good aim or a sheer volume of fire.  The challenges for striking a magazine are many, but the level of protection surrounding a ship’s magazine varies considerably, not only by ship type but also by ship class and within the ship itself.  One magazine may be more exposed than another and most ships have at least two.
The most simple attack to understand are AP Shells.  They can only damage a magazine if the shell detonates inside the module.  Over penetrations cannot damage a magazine.  Penetrations which pass through the magazine but explode beyond it cannot damage the magazine either.  AP ‘explosions’ don’t have a blast radius, so the stopping point of the shell is crucial.  It’s only these direct hits which can attack the magazine’s health pool and prompt a chance to cause a detonation.
Landing hits against a ship’s magazines with AP shells presents some very big challenges.  The direction of shells can change via normalization as it passes through armour plates, so aiming directly at the magazines on a straight path may not be the most expedient way to bulls eye these vulnerable locations.  I can say from experience — trying test hitting magazines with AP shells has been a nightmare.
Normalization is the effect of a shell “biting into” the armour to increase its chances at penetration while changing the direction of its path.  Different size shells have different normalization values and vary from as much as 10º for destroyer-caliber guns to 6º for battleship-caliber weapons.
 Things get a little more interesting with HE ShellsBombs and Torpedoes, in that they all use the same base mechanics.  When one of these attacks hits, it explodes on the surface of whatever it strikes.  There is no physical penetration (lewd! ♥) of any of these munitions.  When these attacks explode, they create a blast effect, which Sub_Octavian called a “splash” (LEWD! ♥), that damages everything within that area equally.  Thus, one HE hit with a sufficiently sized blast could damage multiple modules at the same time.  But let’s let Sub_Octavian explain it when I asked him about HE shells penetrating magazines:
 “Well, technically HE shell cannot explode inside the magazine, as it always explodes right on contact with any surface. So, HE damage to magazines (and other modules) is splash damage. Splash damage is rather simple. Wherever HE detonates, splash area is build around the point of detonation. If any module (internal too) is within it, it is dealt damage. Each shell has splash “penetration”..well, the power of splash. Each module has splash protection. Protection is calculated based on module armor and sometimes, based on nearby armor protecting it. Then, after calculation it can be tweaked for balance reasons (if I remember right, we did increase this protection for some German cruisers many months ago). Splash power is calculated based on shell specs, and may be tweaked too – as well as splash alpha damage and splash radius. If protection is too high (or splash power is too low), no damage is dealt to module. E.g. each time a DD shell explodes near BB magazine it does…nothing. However, BB HE shell may damage DD or even cruiser magazine. If damage is dealt, it is lowered depending on splash protection of the module. Proximity of explosion does not matter here, it only determines the area withing which all modules are checked for splash.”

Animation showing the ‘splash’ effect of an HE surface explosion.  Internal modules are similarly affected but are generally afforded better protection.
Bombs and Torpedoes have particularly large and powerful blast-effects, making it possible for even near misses from bombs and innocent looking bow-hits from torpedoes set off magazines under the right circumstances.  Sub_Octavian was clear that torpedo hits near a Battleship’s magazines do not guarantee module damage there.  Torpedo penetration power is high, but so too is the level of protection around battleship magazines.  Different ships and different parts of the ship will have varying levels of defense.  Experimentation can help uncover these vulnerable areas where they exist (I may have already found two).
Magazine Damage
Magazines themselves vary in size depending on the ship and can be calculated easily.  Each magazine has a number of hit points equal to half the normal hit points of the ship.  Myoko with 39,200hp has magazines with 19,600hp each.  Yamato’s massive magazines clock in at a hefty 48,600hp.  This alone affords larger ships a measure of protection against detonations, reducing the chances of taking a catastrophic hit by simple grace of increasing the number of hits needed to deplete the magazine.  Once combined with more effective magazine protection, it’s no wonder that smaller, ships like destroyers and light cruisers detonate more often.  Aside from these two factors, there’s largely little need for Wargaming to tweak magazine vulnerability– armour and the ship’s size generally takes care of this automatically.
The question then becomes:  How much damage does an individual attack inflict on these magazines?
AP Rounds have the simplest and most direct value.  They inflict their AP Alpha damage.  This is the maximum damage listed of the shell in port.  For example, a Warspite or Hood’s 381mm AP shell inflicts 11,400 damage to the hit points of a magazine.  Atlanta’s own AP shells inflict a rather wimpy 2,100 damage.  Comparatively, AP rounds potentially deal more damage than all other forms of attack on a per hit basis and can be considered a kind of trade off for the challenges of landing hits.
HE Rounds (and Torpedoes and Bombs) have a more complicated calculation.  The amount of damage they do comes (once again) from the “splash” damage Sub_Octavian described, modified by the protection and armour surrounding the magazine.  Thus, this value varies depending on not only your target, but where you hit it and with what type of ammunition.  Note that Bombs, Torpedoes and HE from large caliber guns are much more powerful (and larger) “splashes” making them more effective at damaging magazines than smaller caliber attacks.  This can include near misses of the ship itself in the case of bombs and possibly Battleship HE too (must test this!).
When an attack does damage a magazine, the detonation calculation is taken immediately based on the reduced level of hit points.  In this manner, the size of the attack only matters while there are hit points still remaining in the magazine.  Once the magazine’s health is completely depleted, the amount of damage an attack does is largely irrelevant — only the number of hits matters with each getting the same chance of causing a catastrophic explosion.
Still Fun, Still Engaged
The challenges facing testing this come from a lack of reliable feedback when magazines are actually struck and how much damage they take.  Lert and I just finished sinking 300 Yamato for the next part of our detonation test, each done in batches of 100.  The lessons Sub_Octavian has provided puts the results into a little more context, so now I want to sink at least another 100 before presenting my findings.  I want to thank Sub_Octavian for taking the time to answer my questions.  Stay tuned for more fun (and engaging) detonation revelations.

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