Sensors

Visual Spotting

Visual spotting requires Line of Sight. All units can spot 360 simultaneously except vehicles which can spot in one firing arc per crew member. For submerged units, start on the “Light Fog / …” category and move up one for every 10 depths underwater.

Maximum Visual Range (hexes)
Light/Weather Condition BattleMech/Vehicle+ Infantry Aerospace+++ Large Craft
Pitch Black++ 3 1 5 4
Moonless++ / Full Moon Night++ / Blizzard 5 2 10 8
Heavy Fog / Hail / Rainfall / Snowfall / Sleet / Blowing Sand 10 5 20 15
Dusk/Dawn++ / Snow Flurries / Gusting Rain 15 8 30 20
Moderate Rainfall/Snowfall 20 10 50 25
Light Fog / Hail / Rainfall / Snowfall 30 15 60 35
Daylight (no conditions) 60 30 120 70
Additional Effects Modifier
Light Smoke -1 hex per hex in LOS
Heavy Smoke -2 hex per hex in LOS
Active Visual Camouflage++++ Half distance, rounded down
Void-Sig System Quarter distance, rounded down
Searchlight Changes Nighttime Conditions to 30 hexes

+ Includes grounded aerospace units
+ If unit mounts a searchlight, add 10 hexes; for infantry, add 5 hexes
+
+ Must be between Altitude 2 and 9; if at Altitude 1 (NOE), unit is considered grounded. If at Altitude 10 or higher, the unit cannot be used for visual spotting.
++++ Includes the following: Chameleon Light Polarization Sheild, Mimetic Armor, Sneak/Camo and Battle Armor Camo.

Sensor Spotting

Range (in hexes)
Sensor System Short (2D6=7-8) Medium (2D6=5-6) Long (2D6=2-4)
Beagle Active Probe+ 1-12 13-24 25-36
Bloodhound Active Probe 1-16 17-32 33-48
Clan Active Probe / EW Equipment+ 1-15 16-30 31-45
Clan Watchdog / Light Active Probe 1-9 10-18 19-27
’Mech IR / Magscan Sensor++ 1-10 11-20 21-30
’Mech Radar / Support Vehicle Basic Fire Control IR 1-8 9-16 17-24
Combat Vehicle / Support Vehicle Advanced Fire Control IR/Magscan++ 1-9 10-18 19-27
Heat Sensor+++ 1-9 10-18 19-27
Combat Vehicle / Support Vehicle Advanced Fire Control Radar/Improved Sensors++++ 1-6 7-12 13-18
Support Vehicle Basic Fire Control 1-4 5-8 9-12
’Mech Seismic Sensor 1-2 3-4 5-6
Vehicle Seismic Sensor 1 2 3
Additional Effects (All Sensors except Seismic) Modifier
Castles Brian If along LOS, all sensors except Seismic and Active Probes completely blocked
Hill Hex If along LOS, all sensors except Seismic, MagScan, and Active Probes completely blocked
Electromagnetic Interference -4 to all range brackets
Lightning Storm -1 to all range brackets
Additional Effects (Radar Only) Modifier
Building Hex If along LOS, sensor completely blocked
Additional Effects (IR/Heat Senor/Radar only) Modifier
Heavy Woods/Jungle Hex -1 hex per range bracket per hex in LOS
Ultra Woods/Jungle Hex -2 hex per range bracket per hex in LOS
And Building Hex but Hardened or Castles Brians -1 hex per range bracket per hex in LOS
Hardened Building Hex -2 hex per range bracket per hex in LOS
Castles Brian Hex If in LOS, all sensors completely blocked

Support Vehicles: Support Vehicles without a Basic or Advanced Fire Control cannot use these electronic sensors rules.
+ Includes the active probe mounted on battle armor
+ An infrared unit spots a unit that is “hot” more easily than other units; a magscan sensor spots larger units more easily
+
+ As mounted on battle armor; is used exactly like a ’Mech/vehicle IR sensor
++++ As mounted on battle armor

Airborne Units: Sensor ranges for airborne units do not change, though LOS exists to all units on the playing area. If using a High-Altitude Map, an airborne unit must be in the Ground Hex Row to make a sensor detection roll. If using a Low-Altitude Map, an airborne unit must be at Altitudes 1-9 to make a sensor detection roll. In both instances, the airborne unit is considered to be in Hex 0909 of the ground mapsheet corresponding to the hex occupied by the unit.

Seismic Sensors: A unit must have expended MP (of any type) during the Movement Phase of the turn in which the sensor check is made in order to be detected by a seismic sensor (this includes units landing in a hex after expending Jumping MP.

Airborne units (including units expending VTOL MP) and submerged units (providing they are not moving along the bottom of the water hex) cannot use seismic sensors, and they cannot be spotted by seismic sensors.

If using Planetary Conditions, seismic sensors cannot be employed during any turn that an earthquake or meteor shower occurs on the playing area.

Infrared Sensors: When using infrared sensors, any time a unit that tracks head is “hot”, it can be more easily detected. For each heat-induced MP modifier on the target, the range of the sensor is expanded for that unit(s) by 1 hex; add 1 additional hex if the unit has been hit by an inferno attack, or is standing in a hex that is on fire.

If using Planetary Conditions that affect the temperature of heat-tracking units, also apply the following rules: for each -1 Heat Point applied per turn, the range of the sensor is expanded for that unit(s) by 1 hex; for each +1 Heat Point applied per turn, the range of an IR sensor is shrunk for that unit(s) by 1 hex. Units that are not “hot” cannot be detected by an IR sensor scan.

Magnetic Sensors: If MagScan sensors are being used, any unit (except conventional foot and jump infantry) within range is spotted regardless of LOS, unless a hill or building blocks LOS, in which case the sensor cannot detect the target unit. It can detect a unit through any number of woods/jungle hexes.

When using MagScan sensors, the larger a unit is, the more easily it can be detected. For any unit from 80 to 100 tons, the range of the sensor is expanded by 1 hex. For any unit from 101 to 1,000 tons, the range is expanded by 2 hexes. For any Large Craft or Large Naval Vessel, the range of the sensor is expanded by 3 hexes.

Units that weigh less than 20 tons cannot be detected by a magscan sensor, including all infantry.

If using Planetary Conditions, a magscan will not detect a unit that occupies a Heavy Industrial Zone hex.

Commanders: If using commanders, a sub-force commander can make two different types of sensor rolls, while a force commander can make three different types of sensor rolls (this includes rolling for his own sensors and/or rolling to monitor remote sensors).

Communications Equipment: If a unit on a side mounts 3 to 6 tons of communications equipment or a cockpit command console, once the player has rolled the dice to use a sensor, the player then rolls 1D6. On a result of 1-3, the numerical value below the original dice roll result is added to it; on a result of 4-6, the numerical value above the original dice roll result is added.

If a unit on a side mounts 7 or more tons of communications equipment, once the player has rolled the dice to use a sensor, the numerical values above and below the original dice roll result are also added.

These benefits apply to all units on a side, but the units mounting the equipment must be on the playing area. Additionally, if the communications equipment or cockpit command console loses its Initiative bonuses for any reason the sensor bonuses are lost as well.

Sensors

M.E.R.C.S. Battletech mnem