The M131 Modular Pack Mine System (MOPMS) is a human-portable system used by the United States Army for dispersing a total of 21 anti-tank (AT) and anti-personnel (AP) land mines. The system was specifically created to employ a short-term (temporary) protective, tactical, or nuisance minefield. The unit weighs 165 pounds (~75 kg) so can easily be put in place (even in battle conditions) by 4 men, and can later be activated by remote (hardwired) or radio control.
Employment
Though the system can be activated by wire, it is most commonly and most safely activated by a hand-held remote control unit (RCU) that allows a single operator to control up to 15 groups of MOPMS from as far as 1 click away1. The radio units use coded frequencies to stop electronic countermeasures against the system. Activating the system discharges 17 M78 AT and four M77 AP mines within a 35 meter 180°semicircle radius. The anti-tank mines are magnetically activated so can be triggered without direct contact, while the anti-personnel mines automatically disperse 4 tripwires. By default, all mines will self-destruct after 4 hours2 (remember, this is a temporary minefield), but the timer can be reset up to 3 times for a total of 16 hours3. In addition, all landmines can be set to detonate on command by remote control if needed. This self destruct feature has numerous benefits:
- It allows the Army to easily comply with the Geneva Convention with respect to landmines and minefields by not leaving active mines behind which may harm innocent civilians.
- By detonating on command it can be used as an offensive weapon if needed.
- It can quickly be removed if friendly forces need to get through the area.
In addition to the reasons above, temporary minefields might be used to:
- Close a road or other easily passable terrain feature until reinforcements arrive
- Quickly create a nuisance to attackers during battle
- Set up an ambush (i.e., set it off while an enemy unit is inside the 70 meter diameter of effect)
- Set up a trap (i.e., set it off after a unit has entered an area effectively cutting off an escape route)
- Deploy behind retreating forces to allow a safe getaway
1 Given enough wire, the hardwired unit can be activated up to 3 km away. If multiple systems are daisy chained together, subtract 400 meters for each additional unit.
2 Actual destruct times occur randomly starting around 3 hours and 12 minutes (approximately 80% of full time) and continue until the 4 hours have expired
3 If employed with the hardwired system, the timer cannot be reset or detonated on command, and all mines will self-destruct after the originally set time. | 
