First, the position matters.
When firing on a target, you can hit its Front, Left, Right, or Rear Arc (each 90 degrees) depending on your position relative to the target’s, indicated by the red arc at the base of the target. This arc determines which Locations on the target your attack will be able to damage: An attack on the left arc cannot damage the Right Arm. If you’ve been dealing damage consistently to one Arc of an enemy mech, it’s a good idea to try to continue dealing damage to the same Arc. This will maximize your chance of punching through Armor and damaging the Structure of Locations on that side of the ‘Mech.
Furthermore, Mechs generally have much weaker rear armor than front armor, and Rear-Arc shots ignore Defenses such as Cover and Guarded. Moving or jumping behind an enemy to get a Rear Arc shot is often an effective way to gain the upper hand. Of course, this also applies to your mech. An exposed backside is a threat and the enemy won't hesitate to ram an armored fist right up that mech's tender nether components.
The actual resolution of combat wholly depends on the weapons mounted on your mech. If the enemy is in range, you will be able to engage the enemy. Doing so brings up the attack overlay, showing the current status of the target (mech/vehicle/turret/gardener). The lower right-hand display will show the chance to hit (next to the ammo and weapon damage display), while the mech's status bar will show the projected heat gain. You can choose to deactivate the weapons to tailor the attack to the situation and conserve heat or ammunition.
Accuracy is determined by the game depending on a variety of factors, including:
- The Mechwarrior's Gunnery skill (+5% per point).
- Attacker's class (-10% to hit for Light mechs, 0 for Mediums, +10% for Heavies, and +20% for Assaults).
- Elevation (10% per 15 units; the higher, the better, the lower, the worse; at present, you can only receive a +10% bonus).
How much damage you deal (and of course, the enemy) is determined by the facing of your mech, the weapons used, and the accuracy of an attack. Attacks are distributed along the chassis, unless a called shot was made on a prone or shutdown mech.
Damage can be received as direct damage, heat buildup, or stability.
- Direct damage is subtracted from the subsystems hit: First armor, then structure. If armor and structure is reduced to zero, the affected body part is destroyed along with all mounted systems. If the head, central torso, or both legs are lost, the mech is totaled.
- Heat damage increases the target's hotness, applying standard effects. Bracing at the end of a mech's turn cools it down.
- Stability damage refers to how grounded the Mech is. Mechs which exceed 50% stability damage become Unsteady, taking a penalty to accuracy, while a full bar sends them prone: They are vulnerable to called shots and need to spend move points to get back up. Bracing at the end of a mech's turn reduces stability damage.
In general, a mech needn't be destroyed immediately. All that matters is rendering it combat ineffective: Destroying its mounted weapons is usually enough to render it inert (unless it engages your mechs in melee).