Anti-Jump "Active" Mine
Anti-Jump "Active" Mines are a type of land mine first employed over a millennium ago, although their use waned in the face of less expensive conventional mines. In one regard, however, conventional mines were less effective against units which did not maintain contact with the ground or could avoid it, such as hovercraft, WiGE vehicles, Jump Infantry and jump jet-equipped BattleMechs. Efforts to combat this weakness were further spurred on with the invasion of the Clans and their hordes of jump-capable Battle Armor suits, and of the many nations which sought to solve this problem the Capellan Confederation was the first to re-introduce the "Active" land mine in 3058. 
These mines incorporate a modified and miniaturized version of the Beagle Probe which continually scans the surrounding area to detect units passing overhead. If a jumping trooper or vehicle is detected a small explosive charge launches the mine into the air prior to detonation, whereupon a cloud of shrapnel brings the target down. While effective, units with stealth or ECM functionality can spoof the sensor system, making them harder to detect. The Capellans developed versions of the "Active" mine which could be deployed normally or via special Thunder LRM munitions.
In Total Warfare play, active mines detonate on a 9+ when a jumping unit passes overhead.
- Field Manual: Capellan Confederation, p. 145 "Capellan Confederation Armed Forces Rules - New Equipment - Missile Munitions - Thunder-Active"
- Tactical Operations, p. 364, "Active Mines (Land)"
- Tactical Operations, p. 372 "Advanced Weapons and Equipment - Alternative Munitions - Missile Munitions"
- LosTech: The MechWarrior Equipment Guide, p. 38, "Anti-Jump Active Mine"
- A Time of War, p. 277, "Explosives - Mine Special Game Rules"
- A Time of War, p. 278, "Standard Explosives - Table"