New fragmentation damage model in ToW3: Korea

One of the more frequent player complaints of the previous titles in the Theatre of War series was the high infantry casualty rate. Since battlefields in the series are usually exposed to all kinds of fire, infantry without cover were exterminated quickly and thus their combat value was limited. In reality, even open and level fields usually have many small irregularities, resulting in unevenness of the ground that is sufficient to provide cover for a prone man. In addition, another peculiarity of artillery fire is that high-velocity munitions with shallow flight trajectories are ill-suited for engaging prone soldiers. They have large dispersion along the flight direction (closer-farther) and most munitions don't produce an even sphere of fragments, and in the case of ground-level detonation most of the fragments impact into the ground harmlessly to nearby troops. They produce a so-called "butterfly" cloud of fragments: most of the fragments are ejected to the sides.

Because of this effect, howitzer shells and especially mortar mines, are far more dangerous for prone troops - their blast area is close to a perfect circle because of the nearly vertical trajectory before impact.

In previous ToW games, fragmentation damage was calculated using a spherical approximation, where targets closer to the center of this sphere were more likely to be hit. The shielding effect of the ground's unevenness (terrain underfeature) was also relatively simply modeled - soldier stance (prone, kneel or stand) affected probability of being hit by a fragment without taking this into account (thus a soldier could be killed by a fragment behind a stone fence or a tank, while houses and trenches lowered this probability).

In Theatre of War 3 we decided to get rid of these simplifications and approach the modeling of a fragmentation cloud on a new level of complexity. First, the mathematical model of terrain unevenness was created (see picture below). If a projectile is going to hit a unit, it's height above the ground level is being checked as soon as it is within the (Dist) distance. If it's below a set level Hmin it detonates. If it's above Hmin, but below Hmax, it detonates with a certain probability. Each terrain type has separate Hmax, Hmin and Dist values. Effectively, it works so there is an invisible layer above the ground that provides cover and stops projectiles flying low in most cases.

Second, the fragmentation cloud is no longer a sphere. Now all explosive projectiles have their fragmentation clouds set up using sector limits and probabilities of fragment ejection for each sector. Most fragments are ejected from sector A.

Since the system now takes into account where a target is relatively to the projectile flight path and point of detonation, an obstacle or another unit can shield a target from fragments of a blast. Fragments are being traced to three points if a soldier stands, two if he kneels and one if he is prone. A soldier sitting in a trench now is invulnerable to fragments from detonation that occurred on the ground level, but he can be hit if a projectile happened to fall right into the trench. Keep in mind however that damage from the blast itself (a wave of excessive air pressure) is different to damage from fragments and a soldier in a trench can still be wounded or killed by a powerful blast next to him even if a trench shielded him from fragments completely.

There are some screenshots below that illustrate how new damage systems work by displaying debugging info overlay. They show fragments tracing and results of these tracing calculations. Blue lines show fragments that were not ejected in this direction at all because of low probability.

Green traces - these fragments were cut off by terrain unevenness modeling (they hit the ground hummocks, tussocks and such) or unlucky other soldiers that shielded their buddies behind them.

Red traces - these fragments hit the targets and wounded or killed them.

Typical situation 1a: an artillery shell with a shallow trajectory (white line) detonates near the group of standing soldiers. As you can see, traces along the flight path are mostly blue because there are few fragments ejected this way, most of them have gone to the sides and thus this shell took out mostly soldiers on the left. Some of the troops were hit into all three tracing points (head, torso, legs) while some were hit once or weren't hit at all.

Case 1b shows a mortar mine impact near standing soldiers. It detonated on the ground while falling almost vertically (white line) and ejected a more homogeneous fragmentation cloud because of this. More soldiers were hit in this case.

Now let's detonate an artillery shell near prone infantry, case 2a. The flight trajectory is shallow again. All targets along its flight path are safe from fragments (blue lines), while the "butterfly" cloud hit three guys on the sides (all others were saved by the ground unevenness system that stopped the fragments, their projected traces are shown by green lines). This is a good example of an artillery shell ineffectiveness against prone targets - these three soldiers were wounded, no fatalities happened this time.

Final case 2b: mortar shell detonation near prone infantry. Again, the fragmentation cloud is far more uniformly distributed than the fragmentation cloud of an artillery shell, but most soldiers were shielded by terrain unevenness cover.

As you can see, the improved damage simulation is far more realistic in handling explosions and results in an increase in infantry survivability.