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HE and Overpressure

Work in progress

This wiki is still being written. Pages are incomplete, numbers may change, and some mechanics are not covered yet.

Explosive rounds work on a different rule set. Overpressure is scored against the target vehicle weight rather than its armour, and fragments spray in a full sphere rather than a cone.

A direct hit on armour

An explosive round produces an interior fragment event when its penetration beats the plate's effective thickness, at any angle up to its ricochet gate. It then pays the plate and keeps a floor of a third of its calibre.

bursts inside  ⟺  P>tm,P←max⁡ ⁣(P−t, C3)\text{bursts inside} \iff P > \dfrac{t}{m}, \qquad P \leftarrow \max\!\left(P - t,\ \dfrac{C}{3}\right)
Unlike a kinetic round, the angle only has to clear the ricochet gate rather than beat a line of sight thickness.
NHE=clamp⁡ ⁣((C30)3E+10, 10, 1000)N_{HE} = \operatorname{clamp}\!\left(\left(\dfrac{C}{30}\right)^{3} E + 10,\ 10,\ 1000\right)
E is the shell's explosive multiplier. Fragment count scales with the cube of calibre.

Those fragments spray in a full sphere from the back face of the plate, not in a cone. Each successive fragment pays the entry plate again, so the budget drains as the sphere fills.

Peff=P⋅m⋅OP  −  ∑tcrossed  −  100 g2⏟distance lossP_{\text{eff}} = P \cdot m \cdot OP \;-\; \sum t_{\text{crossed}} \;-\; \underbrace{100\,g^{2}}_{\text{distance loss}}
g is fragment travel in studs. Crew parts are the exception: the distance loss term is dropped entirely for them.

Key idea

That crew exception is the whole reason blast reaches people across a fighting compartment while the same fragments die before reaching a module the same distance away.

Overpressure

Overpressure is a multiplier on the armour weakness value, recomputed at each structural part. It is worked out from the hit vehicle's configured weight, not from the thickness of the plate. Hull parts use the hull weight, turret parts use the turret weight, and helicopters use a fixed value of 3.

OP=clamp⁡ ⁣((C⋅E75)4W3⋅6,  1,  5)OP = \operatorname{clamp}\!\left(\dfrac{\left(\dfrac{C \cdot E}{75}\right)^{4}}{W^{3}} \cdot 6,\ \ 1,\ \ 5\right)
C is calibre, E is the explosive multiplier, W is the hull or turret weight of the target.

Because weight enters as a cube and charge size as a fourth power, the result swings violently with the matchup:

ShellTargetResult
152 mm, E = 13 ton turretabout 3.7
152 mm, E = 140 ton hullabout 0.0016, clamps to 1
The same shell is devastating against a light turret and does nothing extra against a heavy hull. It is a mass matchup, not an armour matchup.

Interactive

Overpressure multiplier

3.75×

Weight is cubed, so the same shell that overpressures a 3 ton turret does nothing at all to a 40 ton hull.

The explosion itself

The blast only runs if an enemy vehicle is within the blast radius plus 20 studs. Radius, damage multiplier and fragment count all depend on the type.

TypeBlast radius (studs)Damage multFragments
HE(C/50)³ + 14.281.6Eclamp(((C/30)³ + 10)E, 10 to 2000)
HESH(C/50)³ + 7.141.0Esame as HE
APHE, HEAT, ATGM(C/50)³ + 3.570.4E, tripled for top attackAPHE: clamp(((C/40)³ + 30)E, 30 to 1000)

Fragments fly out to E((C/40)3+3.57)E\big((C/40)^{3} + 3.57\big) studs, and their penetration falls off linearly with distance from the burst.

Pfrag(g)=P0(1−gm⋅Rblast)+,P0={(C/8)1.3chemical jet burstP⋅max⁡ ⁣(1,(C/100)1.5)HEPAPHEP_{\text{frag}}(g) = P_0\left(1 - \dfrac{g}{m \cdot R_{\text{blast}}}\right)^{+}, \qquad P_0 = \begin{cases}(C/8)^{1.3} & \text{chemical jet burst}\\ P \cdot \max\!\big(1, (C/100)^{1.5}\big) & \text{HE}\\ P & \text{APHE}\end{cases}
The result is floored at a fifteenth of calibre for non-chemical bursts, then multiplied by 0.11 for HESH and APHE, whose fragments are casing splinters rather than a focused charge.
damage=clamp⁡ ⁣((C/24)2+5, 1, 104)4⋅damageMult\text{damage} = \dfrac{\operatorname{clamp}\!\big((C/24)^{2} + 5,\ 1,\ 10^{4}\big)}{4} \cdot \text{damageMult}
Applied to each part a fragment reaches.

Note

Top attack proximity missiles focus the burst into a narrow downward cone of about 10 degrees, with half the fragment count and triple the damage.

Fuses

FuseBehaviour
APHEArms once a contact strips more penetration than its fuse sensitivity, then detonates exactly its fuse delay in metres later
ProximityPast its arming distance, detonates when the flight segment’s closest point to a target falls inside the fuse radius
Top attackAdditionally confirms a target below with a downward ray before firing
The proximity check tests the closest point on the whole flight segment, so a fast missile cannot tunnel past a target between frames.

HESH

HESH follows the same explosive path but with a smaller blast radius and a plain damage multiplier, and its fragments are cut to eleven percent because they are casing splinters. Its ricochet branch also divides speed and penetration by 3 rather than 1.3.

See also