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Weapon & Equipment Information
General Details
Name:  TSEMP Cannon
Type (Category):  Weapon (Energy)
Reference:  Interstellar Operations: Alternate Eras (p. 84)

Tight-stream electromagnetic pulse weapons (TSEMPs for short) were derived from abandoned Word of Blake research based on the original Star League’s Centurion Weapon System project. First introduced by the Republic of the Sphere as a single-shot version, a newer repeating-fire version eventually followed. As the name implies, TSEMPs are basically targeted-EMP weapons, intended to disrupt or even shut down opposing machinery—including BattleMechs—without relying on the harpoon line/fusion surge of Jihad-era tasers. Although their use also tends to interfere with the firing unit’s other advanced electronics, stealth equipment, and targeting systems, the TSEMPs’ effectiveness and reusability eventually rendered taser weapons obsolete.

Game Rules:
TSEMP weapons are only effective against targets weighing no more than 200 tons and only deliver effects against conventional infantry if they are cybernetically augmented (in which case, a successful TSEMP attack is resolved as a standard machine gun, delivering 2D6 burst damage to the unit).

Both the TSEMP Cannon and the one-shot TSEMP (TSEMP OS) deliver attacks in the same manner as standard direct-fire energy weapons, but ignore any effects from specialty defenses (such as heat-resistant and laser-reflective armors or the Blue Shield PDS).

Except as noted above when attacking cybernetically-augmented infantry, TSEMPs inflict no physical damage to a target unit. Instead, upon any successful hit, the attacker makes a second 2D6 roll to determine the effects, applying a –2 to the result if the unit is powered by steam engines, or –1 if the unit is powered by internal combustion engines. An additional –2 modifier is added if the target weighs 100 tons or more. Any modified result of less than 2 is treated as a 2.

The TSEMP Effects Table shows the range of results the roll result required to cause any effects by target unit type. A result of that falls under the “No Effect” range for a unit indicates that the target suffers no significant effect from the attack. A result that falls under “Interference” indicates that the target’s sensors and electronics experience a surge that will apply a +2 to-hit modifier for all weapon attacks and sensor operation checks, while also treating the target unit as though it is operating within a hostile ECM field. A result that falls under the “Shutdown” column indicates that the unit experiences a shutdown effect.

Any effects from a successful TSEMP attack will last until the End Phase of the turn after the target unit was hit, after which the target will resume operating normally. An effect of “NA” means the specified target cannot be affected by a TSEMP attack.

In addition to affecting its target, the unit firing a TSEMP will automatically suffer the effects of a TSEMP-delivered Interference effect on itself (as described above). Furthermore, because the TSEMP Cannon requires time to recharge, the weapon cannot be fired in consecutive turns.

Multiple TSEMP weapon attacks against the same target in the same turn add a +1 modifier to the Effects roll against that target (to a maximum stacking modifier of +4). Each Effects roll resolves separately, so the first TSEMP hit resolves with no stacking modifier, while the second receives a +1 stacking modifier, the third receives a +2, and so forth. This stacking effect only applies to the Effects roll, however; multiple Interference effect results will not stack.
Unit Type Availability
BattleMechsIndustrialMechsCombat Vehicles
Inner Sphere Data (BattleMechs)
Prototype Date:  ~3100
Production Date:  3109
Extinction Date:  
Recovery Date:  

BattleMech Specific Construction Rules
May be mounted on Inner Sphere units in accordance with the following construction rules:
 Not allowed if Fuel Cell, Internal Combustion, Primitive Fuel Cell, or Primitive Internal Combustion is selected for the unit's Engine Type

Damage (Aero)
Range (Aero)
Cost (C-bills)
Weight (Tons)
Battle Value
* (*)
–/5/10/15 (Medium)
* See rules for this equipment

Start Year
End Year
Rules Level

Special Abilities
Tight-Stream EMP Weapons

Special Unit Abilities
The special unit abilities described here are intended for use with the Alpha Strike rule system:
 Tight-Stream EMP Weapons (TSEMP)
A unit with this special ability carries tight-stream EMP weapons (TSEMPs), which function much like an energy-based version of the taser (see above).

As with taser weapons, the numerical value for this special ability indicates the number of TSEMP weapon attacks the unit may attempt per turn.

TSEMP attacks may only be attempted in the unit’s Combat Phase, and may only be directed against targets within the unit’s Short or Medium range brackets on the ground map. (TSEMP weapons are ineffective in airborne combat, but may be part of an air-to-ground attack by fighters so equipped.)

A successful TSEMP attack will have no effect against conventional infantry units, DropShips, or any other units that possess the VLG or SLG specials. For all other unit types, a successful TSEMP attack must be followed by a second 2D6 roll, applying a –1 roll modifier if the target is a BattleMech or aerospace unit, a –2 if the target has the LG special, and a +2 if the target is a support vehicle unit.

If the modified roll result is 8 or higher, the target shuts down for 1 turn. On a 7 or less, the target instead suffers a +1 target modifier for all attacks and Control Rolls required of it for 1 turn. Multiple TSEMP attacks against the same target will not increase these modifiers, but each attack each should make its effects roll as long as the target has not been shut down. TSEMP effects against a target automatically wear off in the End Phase of the following turn.

MegaMek Output → Weapon List:  TSEMP Cannon
MegaMek Output → Critical Slot:  TSEMP Cannon
Record Sheet Output → Critical Slot:  TSEMP Cannon