When an attacker inflicts a critical hit on a target, the target player finds the damaged location on the Critical Hit Table on his ’Mech’s record sheet. He then rolls dice for each critical hit and marks off the damage inflicted on the Critical Hit Table.

Head or Leg Hits: If the critical hit strikes the 'Mech's head or legs, roll 1D6, find the result on the Critical Hit Table and mark off the damaged location. If the critical location rolled cannot take a critical hit or has already been destroyed by a critical hit, roll the die again.

Torso or Arm Hits: If the critical hit strikes the ́Mech’s torso or arms, the player rolls both dice. The result of the first die tells which half of the Critical Hit Table for that location is affected, and the second die result identifies the location hit. The Critical Hit Table for these locations is divided into two sets of six critical slots, labeled 1–3 and 4–6.
The first die result identifies which set of slots takes the hit. On a result of 1, 2 or 3, the shot hits a location in the first set of critical slots. On a result of 4, 5 or 6, the attack hits a location in the second set of critical slots. The result of the second die roll identifies the specific critical slot that takes the hit.
If a location has twelve slots, but a critical hit can only strike the first set (the first six), players can simply roll 1D6, instead of rolling the first die to determine the first or second set of critical slots and then another 1D6 to determine the specific critical slot that takes the hit. If a roll result on the bottom half occurs, the controlling player simply re-rolls. This can occur at any time during the game that all the specific slots in the first or second set have taken critical hits; players can then simply roll 1D6 to save time.
Each weapon and other piece of equipment fills at least one slot on the Critical Hit Table. If the player rolls damage for a slot for which no component exists; a slot that cannot take critical damage, such as endo steel, CASE or ferro-fibrous armor, or a slot that has already taken a critical hit, he rolls both dice again. (On pre-generated record sheets, the words in equipment slots that cannot take critical damage always appear more faint than the words in a critical slot filled with equipment that can take critical damage.)
Some weapons, double heat sinks and other equipment take up multiple slots on the Critical Hit Table. A single critical hit disables any weapon or equipment except the engine, gyro and sensors. (A heat sink critical hit destroys only the specific heat sink hit.) Critical hits on additional slots occupied by the weapon, double heat sink and so on have no further effect, but soak up the critical damage; the critical is assigned to the slot, but no further effects occur.

Transferring Criticals: If all the possible slots in the damaged location took critical hits in previous phases, or if no items in the location can be affected by critical hits, the critical hit transfers to the next location per the Damage Transfer Diagram (this diagram also appears on every 'Mech record sheet). Critical hits to the center torso and head do not transfer. However, if all the possible slots in the damaged location were not hit in a previous phase, any excess critical hits do not transfer and are lost.
For example, during the Weapon Attack Phase of Turn 6, an attacking unit damages the internal structure of a target 'Mech's right torso. The controlling player must immediately roll to determine critical hits before resolving any further weapons fire. The player rolls a 12, resulting in three critical hits. The right torso of that 'Mech mounts two medium lasers, one of which was destroyed during Turn 4, and so one critical hit destroys the final medium laser. The two remaining critical hits do not transfer and are lost. However, during the Physical Attack Phase of the same turn, the same controlling player damages the internal structure of the same target ’Mech’s right torso. He rolls a 10 for determining critical hits, resulting in two critical hits. As all possible slots in the damaged location took critical hits in a previous phase, both critical hits transfer to the target ’Mech’s center torso.

Ammunition If a critical hit destroys a slot carrying explosive ammunition, the ammo explodes. The MechWarrior automatically takes 2 Damage Points as a result of the feedback received through his neurohelmet. In addition, the 'Mech takes damage to its internal structure; CASE does not prevent this damage.
Calculate the total Damage Value of all ammo currently carried in the slot and apply that total to the Internal Structure Diagram (ammunition explosion damage starts the damage resolution process at Step 3, as described on page 122). If the location is not protected by CASE, any excess damage transfers to the internal structure of the next location. For locations protected by CASE, vent any remaining damage without further harm. See Other Combat Weapons and Equipment, p. 129, for details.
A critical hit to an ammo slot only explodes the ammo in that slot. It explodes with a force equal to the ammo’s Damage Value times the shots remaining. Missile ammo explodes with a force equal to the number of missiles remaining times their Damage Value. For example, 1 full ton of machine gun ammo explodes with a force of 400 points of damage (2 x 200), while 1 full ton of SRM-2 ammo explodes with a force of 200 points of damage (2 x 2 x 50).
If an ammunition slot has been emptied (the hash marks of weapons fire next to the slot equal the number of shots in that slot), then the slot takes the critical hit, but no further damage or effects occur.
Because an ammunition explosion damages the internal structure of the location where it explodes, a roll to determine critical hits is necessary.

Arm Blown Off This critical hit occurs when the player rolls a 12 on the Determining Critical Hits Table, if the location hit is an arm, and is automatic (the player rolling the critical hits cannot choose to roll the three critical hits instead). The hit blows the arm off, and the weapons and equipment mounted in that arm are no longer available to the 'Mech. The arm may be picked up and used as a club per the rules for Club Attacks.
When an arm is blown off in this way, any explosive components in that section do not explode.

Cockpit A critical hit to the cockpit destroys that slot, kills the MechWarrior and puts the ’Mech out of commission for the game.

Small Cockpit: A critical hit against a small cockpit has the same effects as for a standard cockpit.

Engine 'Mech fusion engines have 3 points of shielding. Each critical hit to an engine slot destroys 1 point of shielding. As shielding is destroyed, the amount of heat escaping from the 'Mech's fusion drive increases. The first hit increases the 'Mech's heat build-up by 5 points per turn. The second hit results in 10 (total) points of added heat build-up per turn, and the third critical hit to an engine slot shuts down the engine and puts the BattleMech out of commission for the rest of the game. Though XL and light engines take up additional slots (in the side torsos), critical hits to any three engine slots also shut down XL and light engines.
A ́Mech is considered destroyed and out of the game if it suffers three engine hits (remember to count engine slots in the side torso if the torso is destroyed).

Compact Engines: Critical hits against compact engines have the same effects as for a standard engine.

ICE: Engine critical hits on ICE-equipped 'Mechs do not generate additional heat. Instead, the ́Mech's controlling player makes a 2D6 roll to see if the engine explodes, at the end of the phase in which its ICE is hit. Apply a +3 modifier to the target number if this is the second hit, or +6 if this is the third such hit. On a result of 10 or greater, the engine explodes, destroying the unit.
For purposes of game play, three or more internal-combustion engine hits destroy the 'Mech, regardless of whether or not the engine explodes. An ICE explosion destroys the 'Mech but has no effect on other units.

Fuel Cell Engines: Like ICE-equipped 'Mechs, engine hits on fuel cell engines do not generate dditional heat. Instead, roll to see if the damage causes an uncontrolled combination of reactants that results in an explosion, destroying the unit. The rules for ICE explosions above apply to engine explosion rolls for fuel cell engines.

Fission Engines: In game play, fission engines function exactly like their fusion counterparts, but in addition to the normal heat effects of an engine critical hit, a damaged fission power plant also has a detrimental impact on the 'Mech's operator because of radiation leakage. The first critical hit to a fission engine causes the pilot to suffer one hit every six turns (beginning six turns after the turn in which the original damage was caused). A second engine hit decreases this damage interval to one pilot hit every three turns.

Foot Actuator This critical hit destroys the muscle (actuator) in the foot. The controlling player must make a Piloting Skill Roll at the end of the phase in which the critical hit occurred, with a +1 modifier (in addition to any other standard modifiers).
For each foot actuator damaged, reduce the 'Mech's Walking MP by 1 and add a +1 modifier to any subsequent Piloting Skill Roll. (The player must recalculate the Running MP as well; multiply the new Walking MP by 1.5, rounding up.) A Piloting Skill Roll is required whenever the 'Mech jumps; the roll is made at the end of the 'Mech's movement. For each foot actuator critical, apply a +1 to-hit modifier to a kick attack.
These effects are cumulative with other leg and foot actuator damage.

Gyro The gyroscope is a 'Mech's most sensitive piece of machinery. It keeps the 'Mech upright and able to move. The gyro can survive only one critical hit; the second destroys it.
After the first critical hit to the gyro, the controlling player must make a Piloting Skill Roll at the end of the phase in which the critical hit occurred, with a +3 modifier (in addition to any other standard modifiers) In addition, the player must make a Piloting Skill Roll every time the damaged 'Mech runs or jumps, with a +3 modifier; the roll is made at the end of the 'Mech's movement.
When a 'Mech's gyro is destroyed (after a second critical hit), the 'Mech automatically falls and cannot stand up again. The controlling player makes an immediate Piloting Skill Roll, with a +6 modifier for the destroyed gyro (plus any modifiers for other damage), to avoid damaging the MechWarrior during the automatic fall.
'Mechs with a destroyed gyro may make weapon attacks per Firing When Down, and may change facing by one hexside per turn provided they have at least 1 MP available. A 'Mech with a destroyed gyro is not considered immobile.

Compact Gyros: Critical hits against compact gyros have the same effects as against a standard gyro.

Heavy-Duty Gyros: Critical hits against a heavy-duty gyro are identical to those against a standard gyro, with the following exceptions: it takes three critical hits to destroy a heavy-duty gyro. On the first critical hit, a +1 modifier applies to all Piloting Skill Rolls, but no such rolls are required when the 'Mech runs or jumps. Treat the second critical hit to a heavy-duty gyro as the first critical hit to a standard gyro. The third critical hit destroys the heavy-duty gyro with all the standard effects.

XL Gyros: Critical hits against XL gyros have the same effects as a standard gyro.

Hand Actuator A critical hit to the hand actuator destroys the muscles controlling the 'Mech's wrist and hand. Add a +1 to-hit modifier to all punches made with this arm. In addition, the 'Mech can no longer make physical weapon or clubbing attacks with this arm. This effect is cumulative with the effects of destroyed arm actuators.

Head Blown Off A hit blows off a 'Mech's head when the player rolls a 12 on the Determining Critical Hits Table for the head hit location. This critical hit destroys the 'Mech's head, kills the MechWarrior and puts the 'Mech out of commission for the rest of the game.

Heat Sinks One critical hit to a heat sink destroys the heat sink and reduces the 'Mech's ability to dissipate heat. For example, if a 'Mech is designed to dissipate 16 points of heat per turn and three of its heat sinks have been destroyed, it can now only dissipate 13 points of heat per turn.
A double heat sink takes up more than one slot on the Critical Hit Table but is destroyed by a single critical hit.
Additional critical hits to a multi-slot heat sink produce no further effects. Each double heat sink destroyed reduces the 'Mech's ability to eliminate heat by 2 points.
The loss of any heat sinks take effect at the beginning of the Heat Phase of the turn in which they occur, meaning they will not dissipate any heat in the turn they are destroyed.

Hip A hip critical hit freezes the affected leg in a straight position. The controlling player must make a Piloting Skill Roll at the end of the phase in which the critical hit occurred, with a +2 modifier (in addition to any other standard modifiers).
The 'Mech's Walking MP is cut in half (round up). Add a +2 modifier to any Piloting Skill Rolls required, and make a Piloting Skill Roll every turn that the damaged 'Mech runs or jumps. The roll is made at the end of the 'Mech's movement.
The 'Mech cannot make kick attacks. After a hip critical hit, ignore all modifiers from previous critical hits on that leg. This means it is possible for a 'Mech's performance to improve after a hip critical hit if it had suffered previous critical damage to the same leg. Since the leg becomes locked in a straight position, it serves as a sort of crutch, making movement easier in some cases than moving on a number of free-flexing damaged actuators.
A critical hit to the second hip reduces the 'Mech's MP to 0 and adds another +2 modifier to its Piloting Skill Roll target number (the ’Mech is not considered immobile, however).
For four-legged 'Mechs, the fourth hip critical hit reduces the 'Mech's MP to 0 and adds another +2 modifier to all Piloting Skill Rolls.

Four-legged ‘Mechs: A four-legged ‘Mech with a single hip critical loses its ability to ignore the modifier for firing while prone.

Jump Jet When a jump jet exhaust port takes a critical hit, that jump jet can no longer deliver thrust. This decreases the distance the 'Mech can jump. For each exhaust port hit, reduce the 'Mech's Jumping MP by 1.

Leg Blown Off This critical hit occurs when the player rolls a 12 on the Determining Critical Hits Table for a leg hit location hit, and is automatic (the player rolling the critical hits cannot choose to roll the three critical hits instead). When a 'Mech's leg is blown off, the 'Mech automatically falls and takes normal falling damage, though it might be able to stand up again. The leg may be picked up and used as a club per the rules for Club Attacks.
When a leg is blown off in this way, any explosive components in that section do not explode.

Life Support Any critical hit knocks out this system permanently and leaves the pilot vulnerable to increased heat. The other critical location can still take damage, but this has no additional effect.
The MechWarrior takes 1 point of damage every Heat Phase that the 'Mech's internal heat ranges from 15–25, and 2 points of damage for every turn that its internal heat is 26+ on the Heat Scale.
A life-support critical hit also eliminates the 'Mech's internal air supply. If the 'Mech is submerged (in Depth 2 or deeper water, or prone in Depth 1 or deeper water) in the End Phase of any turn, the pilot takes 1 point of damage.

Lower Arm Actuator This critical hit destroys the actuator in the 'Mech's lower arm. Add a +1 modifier to the to-hit number for weapons firing from that arm and a +2 modifier for all clubbing attacks and any punches or physical weapon attacks with this arm.
Damage from punches with this arm is halved (round down).
These effects are cumulative with other arm and hand actuator damage in the same arm.

Missing Actuators: Some 'Mechs are designed without one or both lower arm actuators. These 'Mechs do not suffer the weapon attack modifier for the missing actuators, though the modifiers for physical attacks still apply.

Lower Leg Actuator This critical hit destroys the muscle (actuator) in the lower leg. The controlling player must make a Piloting Skill Roll at the end of the phase in which the critical hit occurred with a +1 modifier (in addition to any other standard modifiers).
For each lower leg actuator damaged, reduce the 'Mech's Walking MP by 1 and add a +1 modifier to any subsequent Piloting Skill Roll. (Recalculate the Running MP as well - multiply the new Walking MP by 1.5, rounding up.) The player must make a Piloting Skill Roll whenever the 'Mech jumps. The roll is made at the end of the 'Mech's movement. For each lower leg actuator critical, apply a +2 to-hit modifier to a kick attack to-hit modifier and inflict half the standard damage (round down).
These effects are cumulative with all other leg and foot actuator damage.

Sensors When a 'Mech takes a critical hit to its sensors, add a +2 modifier to the to-hit number every time the 'Mech fires its weapons. A second sensor hit makes it impossible for the 'Mech to fire its weapons. Critical hits to sensors do not affect physical attacks or other electronic equipment mounted by the unit (such as ECM suites, C3 computers and so on).

IndustrialMechs: The sensors on an IndustrialMech are completely disabled after taking a single critical hit, rather than the two hits necessary in a BattleMech. The other critical location can still take damage, but this has no additional effect.

Shoulder A critical hit to this location freezes the shoulder joint. The 'Mech may not punch or make physical weapon attacks with that arm, nor may it make clubbing attacks, and a +2 modifier applies to pushing attack to-hit numbers for each damaged shoulder.
Add a +4 modifier to the to-hit number for all weapon attacks made with weapons mounted on that arm. After a shoulder critical hit, ignore all other weapons fire modifiers from critical hits to that arm.

Upper Arm Actuator This critical hit destroys the actuator in the 'Mech’s upper arm. Add a +1 modifier to the to-hit number for weapons firing from that arm and a +2 modifier for all clubbing attacks as well as any punches or physical weapon attacks with that arm. Damage from punches with the arm is halved (round down).
These effects are cumulative with other arm and hand actuator damage in the same arm.

Upper Leg Actuator This critical hit destroys the muscle (actuator) in the upper leg. The controlling player must make a Piloting Skill Roll at the end of the phase in which the critical hit occurred, with a +1 modifier (in addition to any other standard modifiers).
For each upper leg actuator damaged, reduce the 'Mech's Walking MP by 1 and add a +1 modifier to any subsequent Piloting Skill Roll. (Recalculate the Running MP as well - multiply the new Walking MP by 1.5, rounding up.) The player must make a Piloting Skill Roll whenever the 'Mech jumps. The roll is made at the end of the ’Mech’s movement. Kick attacks made with the affected leg have a +2 to-hit modifier and inflict half the standard damage (round down).
These effects are cumulative with all other leg and foot actuator damage.

Weapons and Equipment Weapon systems are surprisingly delicate, and so a single critical hit disables a weapon or other internal component. Though some weapon systems occupy more than one slot on the Critical Hit Table, the first critical hit knocks out the weapon. Additional critical hits to a multi-slot weapon have no further effect, other than to make the equipment more difficult to repair. For example, a particle projector cannon fills three critical slots. However, the PPC is disabled as soon as one of its three critical slots takes a hit.

Explosive Components: Certain non-ammo components such as gauss rifles can explode when they suffer critical hits. The specific rules for the equipment state whether this is the case, and how much damage is inflicted. These explosions are handled in the same way as ammunition explosions.