Iron Wolf Games

In previous posts I have introduced two methods of tracking movement in a science fiction themed D&D campaign. The mech battle, which is virtually the same as one done on foot but at a different scale, and the lightning battle, which emulates an aerial or space dogfight. The chase battle is more complex than either of these.

For the most part, a chase battle runs like one done on foot; vehicles move relative to each other at similar rates, and combat rounds are executed normally. The big difference is terrain.

In a chase battle, combatants are assumed to have matched their speed and trajectory closely enough to stay relatively close together as they move and engage each other. However, they are still moving at great speed, and so stationary objects, or objects moving at a different speed and trajectory, pose hazards to the combatants.

Setup
When tracking a chase battle on a grid, the first step is to determine which ship or ships are the smallest. Refer to the article on vehicle scale for examples. The smallest ship (or obstacle, at the DM’s discretion) takes up one square on the grid, as the blue ship in square K4 above. If the blue ship’s size category were 6, then the yellow one (F6) would be size 7, as it takes up 2 squares. The asteroid in N2 fills about 4 squares, making it size 8, and the green ship (E4) fills approximately 8 squares, making its size 9 (note how doubling the squares increases the category by one).

For battles which cover a lot of terrain, a focus point may be chosen, around which the other objects will move relatively. The largest object is often the best choice for this role, as it is the most difficult to maneuver. On this object’s turn, all other objects and any terrain features should be moved instead of the focus object. Alternately, the terrain can have its own initiative – 0 for basic terrain or roll separate initiative for mobile obstacles.

Movement
Each vehicle in an aerial or space battle is considered to be moving, but what really matters in a chase battle is relative movement, or acceleration. When vehicles in a chase battle accelerate, they move up to their movement in a straight line only. Some vehicle feats may allow exceptions to this rule. Vehicles typically must face in the same direction to remain in combat, especially in aerial or ground-based chase battles. Vehicles properly equipped (via feats/features) may attempt bull rushes, trips, and grapples as a player would.

Obstacles
This is the most dangerous and most unique aspect of a chase battle. When you’re flying through the air or speeding across a landscape, you may encounter objects which, though they may actually be stationary, are moving at a high relative velocity to your vehicle.

Tracking obstacles should be done with progressive markers indicating where the object will be two turns in advance. Note the asteroid in the illustration above; its actual position is N-P:2-3, but its future positions have been projected so that players can see its path for two rounds in advance. Each obstacle has an initiative (rolled or 0 per the DM’s discretion). A vehicle suffers the effect of an obstacle if it lies between that obstacle’s current position and its next one on the obstacle’s initiative. (Note: a piece of yarn may be helpful in determining the exact path of a large obstacle.) An obstacle may have stealth due to its composition or through technological means; these obstacles are only visible one turn in advance. An extremely large obstacle (one that cannot be avoided, for instance) might be visible as many as ten turns in advance, especially if it has an impact rating.

There are several types of obstacles which you might face in a typical chase battle.

A skid obstacle may be a patch of gravel, ice (L2-3 below), oil, etc. Skid obstacles are usually encountered only in ground-based combats.

For each point of skid rating an obstacle possesses, the vehicle’s maneuvering speed is reduced by that number for each square it passes through until it regains control. A vehicle may attempt to regain control using the same action it uses to move at its reduced speed. When the vehicle spends a move action to regain control, it does so automatically unless the skid rating is greater than the vehicle’s maneuvering speed, in which case it must spend a second move action to negate the remaining skid points.

For example: a vehicle has an acceleration rating of 5 (6 base, -1 armor penalty) and skids through 3 squares of an obstacle with skid rating of 2, totaling 6 skid points. Upon spending a movement action to regain control, the vehicle’s acceleration rating negates 5 of the skid points, leaving 1 skid point and preventing the vehicle from moving from its square. If it spends a second movement action regaining control, it will be left with 4 points of acceleration it may use to move across the field.

A slowdown obstacle may be rocks (B3 above), jagged terrain, water (H-I), traffic barriers (N2-4), etc. Slowdown obstacles are usually encountered only in ground-based combats.
Each square of this type of obstacle has a slowdown rating. For each square of this type of obstacle a vehicle passes through, it is pushed backward one square for each point of slowdown rating the obstacle possesses. As an immediate reaction, the vehicle may spend acceleration points to negate points of slowdown, at a one-to-one exchange. It may only negate a number of points of slowdown up to its acceleration rating; it must move backward if any points of slowdown remain. If it chooses to exercise this option, the vehicle’s total allowed acceleration during its next turn is reduced by the number of points of slowdown it negated, and it is automatically assumed to have spent a movement action during that round.

For example: a vehicle with an acceleration rating of 6 drives through 2 squares with skid rating 1, and spends 2 points of acceleration to remain in place during the obstacle’s turn. On its next turn, since it must spend its movement action anyway, it decides to accelerate its 4 more allowed spaces to move ahead of its previous position. If it chooses to sacrifice its standard action and accelerate another 6 squares, this second movement action is not penalized by the slowdown.

Impact obstacles are solid objects which do damage to vehicles upon collision. An impact obstacle may be a wall, an asteroid, a prone or stationary vehicle (such as that in E5-7 in diagram 2) or even a pedestrian. Impact obstacles are a possible hazard in any type of chase battle.

Each impact obstacle has an impact rating. Unlike skid and slowdown obstacles, a vehicle may not pass through an impact obstacle with a rating higher than 1. Instead, it may only continue moving forward if it spends acceleration (as an immediate reaction, per slowdown restrictions) to go around. If it cannot move around the obstacle with its acceleration rating, it falls prone (see Collision section below for rules on falling prone during a chase battle). For each point of impact a vehicle takes, it suffers 1d6 points of impact damage and 1 point of slowdown (which may be negated normally). In the case of low- or zero-gravity combat, treat slowdown as a push originating from the impact obstacle. Colliding with an impact obstacle with a low impact rating, such as a road block, may destroy the obstacle.

Mobile obstacles may be heat seeker mines, stray animals, swinging doors, or even suicidal pedestrians. Mobile obstacles are possible a hazard in any type of chase battle.

Some mobile obstacles have an impact rating just like an impact obstacle, but they are also hazardous to vehicles passing by on either side. When collided with, they do melee damage (in addition to their impact damage) and may also damage vehicles in adjacent squares. When attacking an adjacent target, a mobile obstacle must make a melee or burst attack. Making this attack usually destroys the obstacle just as an impact would, after which it no longer poses a hazard to other vehicles. A mobile obstacle’s attack and damage rolls should be determined independently of its impact rating; experience from mobile obstacles should be equivalent to that of a minion.

Weapons stations may be snipers, mobile turrets, guys with water balloons, etc. Weapon stations are a possible hazard in any type of chase battle.

Like mobile obstacles, a weapon station may have an impact rating, but its main danger is its ranged attack. Weapon stations are usually directed intelligently, and may make their attack or attacks against any target they choose. They are not damaged making an attack, but may be destroyed or disabled by an impact with a moving vehicle, or by taking damage from a vehicle’s weapons. A weapon station’s attack and damage rolls can be determined independently of its impact rating; experience given should reflect its attack, its damage, and its stationary nature.

Collisions
If a vehicle is forced into a square occupied by another vehicle by an effect, obstacle, etc., both vehicles roll a save. A successful save allows the vehicle to choose an available adjacent square and move into it. Failing this save causes a vehicle to fall prone. If a vehicle falls prone in a land- or air-based chase battle, it falls behind and must spend its next turn catching up. If a vehicle in a low- or zero-gravity chase battle falls prone, it remains in its space and must spend a move action to recover before it may accelerate again. Exceptions: if the colliding vehicle is two or more size categories smaller than the vehicle it collides with, the larger vehicle is treated instead as an impact obstacle with a rating equal to the number of movement points the smaller vehicle had left to move when it collided.

For example: a fighter (size 4) was forced by another vehicle’s power to move three squares, but failed its save and collided with a Tesaad freighter (size 6) which was two squares away. Since the fighter had only moved one square before colliding, it treats the freighter as an impact obstacle with a rating of two, taking 2d6 impact damage and 2 points of slowdown. The freighter does not make a save and does not take damage.

Experience
Experience is granted for obstacles in a combat in much the same way it is for traps and other battlefield hazards. For each size category larger the obstacle is than the base vehicle on the combat scale, treat the obstacle as one additional creature when calculating experience. Note that damage is directly tied to an obstacle’s hazard rating; hazard 1 does 1d6, hazard 2 does 2d6, etc. If your obstacle does not do impact damage, halve the experience it grants.

Tags: D&D 4E, D&D 4th Edition, Sci-Fi, ships, Vehicles