'What the hell do you mean by "mines, antipersonnel … slightly used" - where the fuck do you get a "slightly used" anti-personnel mine?'
'These ones, Angola I think … the UN dig them out of the ground and I buy them from a local dealer'. We've had to source some after-market fuses…'
Basic Information
A landmine is a contact activated explosive device designed for use as an area denial weapon. "Contact" may include tripwires, magnetic influence and other remote triggers, but requires the target to activate the device - if it is triggered by the user, rather than the target, it is not properly considered a mine (devices such as the M18 Claymore and the MON series devices are borderline as they can be fired either by tripwire or by command detonation depending on how they are set up).
A traditional separation within landmines is the anti-personnel/anti-vehicle divide, although some authorities consider that the real divide is between soft and hard targets as the difference between an enemy infantryman and a soft-skinned vehicle is, holplogically, smaller than that between a soft-skinned vehicle and an AFV. Anti-personnel mines start with what are known as "toe poppers" - small devices which contain only enough charge to remove part of the foot (although in practice blast effects, especially when channelled by a combat boot, can mean the loss of most of the lower leg) and can be improvised with a single cartridge and a nail. Large blast mines can attack both infantry and soft-skinned vehicles (as above) and may even be able to immobilise lighter AFVs - this was typical of older, WW2 era mines. Alternatively an anti-personnel mine can be designed to spray fragments over a wide area, leading to numerous infantry casualties - these include the infamous class of bounding mines which, when triggered, fire their bursting charge upwards to detonate a meter or so above ground level, hitting their targets in the abdomen and groin.
Anti-vehicle mines tend to be simply very large blast mines, usually with a trigger specifically designed so that it will not be set off by foot traffic - improvised versions have been (and continue to be) made from repurposed artillery shells and aerospace bombs, but purpose designed examples can get quite elaborate. Alternatively an anti-armour mine can be made up of a horizontally acting, single use anti-tank weapon which fires at the vehicle which triggers it. These are often called off-route mines as they are typically positioned to fire laterally into their target, for optimum profile, to take advantage of weaker side armour and due to the fact that there are limited opportunities to conceal such things effectively when they are right in the path of an AFV. A by now somewhat old fashioned technique for using anti-vehicle mines is known as the daisy-chain, whereby an operator drags one or more mines into the path of an enemy AFV at the last possible moment so that it cannot avoid running onto them. This sort of behaviour was considered less than safe in WW2 - by the modern era of tougher AFV and bigger mines it is more or less confined to the realm of anti-armour suicide bombing.
A few non-explosive classes of mines have existed historically, although rarely in great profusion, with incendiaries being quite a big chunk of them (a device designed to meet a potential Nazi invasion of the UK involved a 55 gallon drum of petrol, although it appears not to have entered series production). Entry level members of the category may also include less lethal types such as noise makers or trip flares designed to alert the target's presence rather than inflict damage.
The single most popular way to remove mines is to trigger them in a user-safe manner - either by setting off a large explosion, the shockwave of which propagates through the ground and triggers the mines, or by hitting the trigger with something either resistant or disposable (options vary from steel flails attached to an AFV, to disposable livestock or personnel). Less popular is hand-clearance which involves searching the area for mines and then digging them up and either defusing them or destroying them by controlled detonation. This is hair-raising for anti-personnel mines, and scarcely less so for antivehicle devices which, although designed not to react to human traffic, are often fitted with anti-handling devices precisely to prevent this or co-sown with anti-personnel mines for the same purpose (or, indeed, both). Actually finding the mines can be tricky - older versions were simply found by detecting the metal case, but modern plastic cased designs require the detection of tiny amounts of metal required for the firing circuit (and thus the detectors are prone to false positives) or other techniques, for example detecting the vapours given off by the explosive filler. This sort of search can be done mechanically or by trained scent animals, traditionally dogs but recently rats and even insects have been trained to sniff out mines. Conversely anti-personnel minefields have often had the occasional anti-vehicle device added to inhibit mechanical clearance. Triggering for anti-vehicle mines can also be designed so that, for example, the trigger is placed beyond the mine itself at roughly the length of the enemy's known mine flails so that the flails strike the trigger and detonate a mine under the flailing vehicle. That said, if clearance can be managed, those skilled or foolhardy enough to do so now have a mine, which they can re-lay or scavenge for explosives and related parts.
Responsible users lay mines in clearly demarcated fields, mainly as a passive barrier to enemy movement, and keep records of what they have laid. Less responsible users lay mines promiscuously - and in certain ground conditions, even properly laid mines may not stay put (the Falklands War provides a good example - whilst the Argentinians may not have been stellar exemplars in their staff work, the many minefields they laid were at least professionally planted according to NATO doctrine. Unfortunately many of their records were lost due poor admin and the chaos of the surrender. Also the soft, wet peat of the Falklands allowed many mines to "float" long distances from where they were meant to be). Also, whilst clearance of minefields is often part of demilitarisation at the end of a conflict, this may not always occur and whilst a marked and fenced minefield is (assuming the mines stay put) mostly only a hazard to the stupid, careless and terminally nosey, unmarked mines can remain a hazard for decades afterwards. Such mines typically cause significant and unnecessary casualties amongst local civilians and may make farmland or productive woodland unusable for a prolonged period. Children may be at increased risk, partly because they will often enter areas where adults do not routinely set foot, partly due to a tendency to fiddle with unknown objects and partly because a charge which might only take an adult's foot off can do a lot more harm to a smaller body with its vital organs closer to the blast. Several nations - notably Afghanistan, Angola and Cambodia - have generation long unresolved issues with stray mines, both those laid incompetently and those deliberately dispersed as a terror weapon. This has lead to several campaigns to introduce "international laws" - or at least treaties - against the use of landmines (or, more typically, anti-personnel landmines) which many states, having no particular use for such things. have seen fit to accede to. More pragmatic powers have declined to conform, seeing that they may need such devices at a future date, but still typically refrain from using them under normal conditions. Also, an increasing number of designs include a maximum lifespan feature whereby the mine will automatically detonate after a set period, thus ensuring that at least a majority of such weapons will self clear in time.
Mines share conceptual space with booby traps and a shared ancestry with their command fired relatives. Other conceptual similarities can be found and left over mines come into the category of unexploded ordnance. Presumably in a fantasy setting applications of ward magic and/or various damaging charms will merge into this category. Sci-fi mines are likely to be more or less similar but may have more exotic payloads, discriminatory targeting AIs and possibly even a degree of motility.
When these things put to sea, they become naval mines instead. Attempts to deploy mines into the air have generally degenerated into farce and may or may not be implicated in the loss of HMS Hood, but presumably the naval mine will have some kind of descendant once space combat starts being a normal activity. They are not to be mistaken for the sort of mine that is the result and venue of mining although their ancestry links them to that as well.