Prisoner of war

A prisoner of war (POW) is a person, either a civilian or combatant, who is held in custody by an enemy power during or immediately after an armed conflict.

San Hieronymo personnel
During FOX's occupation of the San Hieronymo Peninsula, Roy Campbell was taken prisoner as the sole survivor of the Green Beret unit sent to investigate the region.

Peace Sentinel
Peace Sentinel kept various prisoners of war in their bases, the majority of whom were Sandinistas, although a few had no prior ties to the FSLN. At least one of whom was also a former American soldier whom the Soviet soldiers held captive when they took over the U.S. missile base in Nicaragua, also wounding him.

Militaires Sans Frontières/Outer Heaven
While recruiting potential allies during the Peace Walker Incident, the Militaires Sans Frontières would imprison those soldiers who were reluctant to join immediately, in the brig on Mother Base. KGB spy Vladimir Zadornov was also taken prisoner by MSF after his involvement in Peace Sentinel's plans was exposed, as well as his attempt to kill their commander Big Boss.

In 1995, Outer Heaven began taking members of the local Resistance as prisoners, including Jennifer's brother. He, along with two other prisoners, were later used as human shields by the mercenary Dirty Duck during his fight with Solid Snake. Snake had earlier allowed himself to be captured by Outer Heaven forces in order to locate Gray Fox, who himself had been taken prisoner during Operation Intrude N312. At least one POW was aware of Big Boss being the leader of both FOXHOUND and Outer Heaven, and warned Snake of this when rescued by the latter.

United States Naval Prison Facility (Cuba)
Sometime during the 1970s, the Naval Prison Facility on the southern tip of Cuba had been converted into a black site by the CIA, with influence from Cipher, to endlessly torture various "enemies of the state." Several of the prisoners were also dissidents from the East who had defected to the West that were captured and then had a brief layover there while in-transit for the other side of the Iron Curtain. Various intelligence agencies from all other the world issued interrogations on the prisoners, including the MI6, the BND, the ISI, and even at least one Soviet intelligence officer. In addition, as insurance none of the prisoners escaped, they had bolts installed onto their achilles' tendon (with the exception of Paz Ortega Andrade who had her feet shackled), rendering them immobile, as well as littered the perimeter of the facility with landmines of both Cuban and American origin. One of the prisoners was an Intel Team agent of MSF who got captured.

In early 1975, the Naval Prison Facility on the southern tip of Cuba held various prisoners, including Chico. Big Boss was dispatched to rescue Chico and Paz. In addition to them, he also rescued several prisoners during his mission there.

Red Army
The Red Army took various prisoners during their invasion of Afghanistan in the 1980s. One prisoner were Kazuhira Miller, who had been caught in an ambush and left the sole survivor.

Mozambique
Gray Fox was taken prisoner and tortured as a RENAMO soldier during the Mozambican Civil War, until Big Boss broke him free.

Iraq
Liquid Snake was taken prisoner by the Iraqis during the First Gulf War, and remained as such until he was rescued by U.S. forces in 1994.

Middle Eastern militia
Middle Eastern militiamen fighting against PMC forces in 2014, sometimes captured enemy Praying Mantis soldiers, who would then be taken to a safe house.

Pieuvre Armement
Some South American rebels were captured by Pieuvre Armement in 2014. Some were captured at the Cove Valley Village, where they awaited execution, while others were detained in a confinement facility near the Vista Mansion.

Desperado Enforcement LLC.
During the Abkhazian Coup in 2018, the Chechen terrorist Andrey Dolzaev's hired PMC, Desperado Enforcement LLC., discovered two civilians who failed to escape the city. The first, nearing the entrance to the city, upon being caught by Desperado, they informed him that the area was off limits, before immediately deciding to just off him. The second, nearing the gate to the old Soviet-era hotel, ended up being suspected of being a Russian spy due to getting caught in what was implied to be an obvious place, and then deciding to waste him in case he is, and then fill out the paperwork. However, Raiden managed to save the hostages before they could do anything to them.

Unconfirmed usage
McDonell Benedict Miller, was captured by the Vietnamese during the Vietnam War and interrogated as a prisoner of war, before eventually escaping and decapitating the head interrogator.

During the Liberian Civil War, several members of a Liberian terrorist cell, responsible for killing American soldiers, were captured by a then-teenaged Solidus Snake. He then proceeded to have one of the child soldiers under his command at the Small Boy Unit, Jack the Ripper, decapitate ten of them as the former's "birthday present" to the latter.

Behind the scenes
Prisoners of war are often featured as characters in the Metal Gear series, with the player having the option to rescue, and in some cases, recruit them.

In both the original MSX2 and the Nintendo Entertainment System version of Metal Gear, the player has to rescue a large percentage of the prisoners to gain Jennifer's trust and allow her to answer Snake's calls. In addition to thanking Snake, some of the prisoners will also supply hints to the player as to how to proceed next. Rescuing the prisoners also results in the player's rank increasing, which also allows for increased health and ammunition counts.

The next Metal Gear game to utilize prisoners of war was the non-canonical sequel Snake's Revenge. Like in the first game, rescuing them will allow the prisoners to offer hints on how to get through areas, as well as rank increases, although unlike the first game, they aren't completely necessary to complete the game outside of rank increases. The manual referred to them as POTs (prisoners of terrorism).

The concept of prisoners of war as a gameplay element was not canonically used again until Metal Gear Solid: Portable Ops, where the player can locate prisoners and rescue them, recruiting them in the process, after the Spy Unit supplies a spy report relating to their imprisonment. In the expansion pack, Metal Gear Solid: Portable Ops Plus, the maps of the Infinity Mission mode sometimes includes prisoners of war to rescue. The locations of the prisoners are indicated by an icon resembling cage bars. Depending on the character model type, Roy Campbell's reaction to a prisoner's discovery will differ. If the prisoner either used the regular enemy character models (e.g., the prisoner was one of the FOX soldiers, one of the Soviet soldiers [barring Jonathan], one of the Soviet officers, one of the scientists/medics, one of the mechanics, one of the Gurlukovich Mercenaries, one of the SEALs, one of the Tengu, one of the Genome Soldiers, or one of the Hi-Tech soldiers) or Johnny, Campbell will identify them as an enemy prisoner that needs to be rescued. If the player finds a unique character (i.e., any of the main characters from Portable Ops, plus Old Snake and Raiden), he will instead either ask them what they were doing there as if they had gone AWOL from FOXHOUND or act as if they survived what was implied to be a very lethal operation that was believed to have killed them, before informing them to return to the truck.

In Metal Gear Solid 4: Guns of the Patriots, Solid Snake could rescue prisoners of war in the Solid Sun chapter at the Cove Valley Village and the Confinement Facility, the former event results in the soldiers repaying the effort by unlocking several sheds for the player to stockpile. Both instances also result in increased affinity in regards to the soldiers. The Piggyback strategy guide also claimed that rescuing the Confinement Facility POWs will result in an additional two guerilla soldiers accompanying Snake but this doesn't happen in the game.

In Metal Gear Solid: Peace Walker, the player can fulton several prisoners of war and recruit them into MSF. The prisoners are identifiable as characters in yellow jumpsuits with the letters "P.S." on the back. When the player is in close proximity to a prisoner of war during gameplay, they will make a grunting noise. When they are fultoned out, they will either cheer or shout "Wohohoho!" Similarly, fultoning female prisoners of war will also have Kazuhira Miller give a different response to their retrieval. Upon being recruited, they are identified as having the symbol "POW" near them with a gold background. Several Extra Ops missions also have rescuing prisoners as being a required element of successfully completing the mission.

In Metal Gear Rising: Revengeance, there are four civilians that the player could rescue who are being harassed by Desperado/World Marshal, two in Chapter R-01, one in Chapter R-03, and one in Chapter R-05. Rescuing them all will reward Raiden with the trophy/achievement "Humanitarian Aid." However, the ones in Chapter R-01 are the only ones that actually come close to the definition of a POW, as they were discovered and held captive by Desperado immediately after an armed conflict before they could escape Sukhumi.

In Metal Gear Solid V: Ground Zeroes, one of the main points of the Ground Zeroes mission was to rescue Chico and/or Paz. In the TGS 2013 nighttime demo for the game, Big Boss also rescued another prisoner in a case of mistaken identity regarding Chico. A leaked achievement/trophy list for the Xbox 360/Xbox One versions also revealed that the player can also optionally rescue prisoners in two missions. In addition, a trial artwork was also unveiled by Kojima, titled POW Rescue, which depicted Big Boss hoisting a POW over the shoulder while in front of an MSF-class Hind D. The requirements of unlocking the artwork are to extract 10 prisoners within the time allotted in a mission that is not in the final version of the game. All the missions in the game save for the system-exclusive extra ops and Intel Operative Rescue will give the player the option of rescuing POWs, in some cases besides the required ones. In the case of the extra op mission, there either aren't any POWs to rescue at all (Jamais Vu) or there are POWs, but they can't be rescued and instead, they will trigger a cutscene when the player attempts to, resulting in their death from FOXDIE (Déjà Vu).