The purpose of these rules is to offer a simpler method of resolving combat in the Inner Sphere at War strategic game without utilizing the Abstract Combat System, allowing a turn's combat to be resolved with no more than two dice rolls and some light math, and making it practical to conduct large scale campaigns.
Anyway, the basics:
The metric being used to measure the strength of each unit is their point value as determined by the Abstract Combat System (ACS). These should be totalled for either side, and further divided into aerospace and ground points. Though their points will add to the defender's total, any points for basic garrison units should be tracked seperately from any other units.
The result of combat is determined using the infantry vs infantry action table found on page 205 of tactical operations, with the previously determined point values standing in for your marine points. Only one roll is made for each phase per turn.
The battle is divided into two phases, "Orbital" and "Planetary".
Orbital Phase
The Orbital phase will only take place in three situations.
1) If the defender chooses to contest the landing of the attackers.
2) If either side chooses to contest the arrival of reinforcements for the other side.
3) If one side chooses to contest the withdrawal of the other.
During the orbital phase, the defender always takes the full damage listed. The P result and halving of damage is not used.
During the Orbital phase, the attacker's total point value is the sum of their aerospace and ten percent of their ground points. When resolving damage, the total damage sustained is applied to aerospace forces first, with the remainder going to any present ground forces only after those aerospace units are destroyed (any damage that does make it through to the ground forces is applied BEFORE the ground unit's points are converted back for the planetary phase).
The Defenders may choose to commit as many points of aerospace forces as they desire and are under no obligation to use all of them. They may NOT use ground forces during the Orbital phase.
An R result means the attacking force has been defeated in orbit and must move out of the system at the first opportunity.
Though the majority of these rules deal with the initial invasion of the attacker, they are also used to deal with the arrival of reinforcements or the withdrawal of one side or the other. This can be handled with the following modifications.
1) Resolve arriving reinforcements from one side or the other in the same manner as the initial invading force, with the addition that any aerospace forces already on the ground may be added to the fight. In this case the arriving forces are treated as the attackers while their opponents are the defender. If BOTH sides have reinforcements show up on the same turn, then randomly determine the attacker and defender in that case, and treat any P results (previously unused in the orbital phase) as R results. In either cases, an R result only applies to the arriving force, not any forces already on the ground.
2) If one side decides they've had enough, they may attempt to withdraw at the start of their turn. The planet's basic garrison cannot be withdrawn. If the other side chooses to contest the withdrawal, resolve in the same manner as a typical Orbital Phase with the withdrawing party functioning as the attacker. A result of R means the withdrawal failed and the unit remains on planet.
Planetary Phase
Upon the conclusion of the Orbital Phase (and assuming the attackers were not repulsed), the attackers may choose to move on to the Planetary phase. This is not required, and the attacker is free to withdraw in the same turn without having to go through another Orbital phase, as long as they move out of the system at the first opportunity.
During the Planetary phase, the total point value of each side is the sum of both ground and aerospace points. Any damage sustained in combat is applied in equal percentages to each seperate unit (thus if a defender has ground, aerospace, and garrison troops and takes 20% damage, each unit loses 20% of its strength).
A result of R means the attacker has been driven from the planet's surface. They may either withdraw completely on the next turn or attempt another landing. In either case, the attackers are subjected to another orbital phase with one additional modification. Should the unit be attempting to withdraw and recieve an R result, they are simply eliminated.
In accordance with the standard Infantry vs Infantry rules, the defenders in the Planetary phase take half damage until a P result is achieved. In addition, if the defending forces are exclusively garrison troops, a P result during the Planetary phase results in the defender's surrender.
Subsequent Turns, Winning, and Losing
Subsequent turns continue in the same fashion until one side is either eliminated, chooses to withdraw, or surrenders. Beyond a garrison unit surrendering on a P result in the Planetary phase, no mechanics for surrender will be offered. Wing it.
