This post originally appeared on Matt Weise's blog Outside Your Heaven.

MGS3 was the moment when the Metal Gear series transformed from refining its core concept (military espionage) to expressing new concepts (mortality, survival, etc.). It did this by taking the ever expanding system of actions, goals, and behaviors built up over the course of four games (MG1, MG2, MGS1, and MGS2) and re-organizing them along the contours of a particular theme (surviving nature) which grew out of a particular setting (a sprawling wilderness). The following games in the series follow the same basic design exercise, of choosing a setting and theme and allowing them to guide the rearrangement of familiar elements into a new system of meanings that make the game "about" something new.

Metal Gear Solid: Portable Ops (PSP 2006) looks almost identical to MGS3 at first glance. A budget sequel made on a portable platform, it reuses a large amount of art and gameplay elements from its immediate predecessor. Yet the way these things are reconfigured makes the ultimate experience quite different. MPO boasts almost all the same core actions as MGS3, including interrogation. In this game however interrogation takes on a whole new meaning. Interrogated soldiers now give two kinds of information, expressing either loyalty or disdain for their commander. If they are disdainful you can knock them out and drag them (like in MGS2/3) to an extraction point. Once extracted, they will "join" your cause, becoming playable characters in future missions. You can recruit loyal soldiers as well, but they take longer to "convince" to join your cause.

Time, unlike in previous Metal Gear games, is an important part of MPO. Instead of a single, on-going "mission" MPO is broken into several smaller "missions" accessible from a map screen. Going on a mission shifts the clock forward 12 hours, turning day to night or night to day. This day/night cycle has implications for many traditional Metal Gear mechanics, including sneaking and stamina. The camo system from MGS3 is gone, but now visibility is determined by time of day. Night missions provide better cover than day missions, and stamina is replenished not by living off the land but by resting. Players can choose to "wait" a 12 hour cycle in order to replenish stamina. (After all, running three missions in a row means you just went 36 hours without sleep.) The same low-stamina effects from MGS3 remain (shaky aim, etc.) but they require different strategies to deal with. Food can replenish stamina, but since MPO takes place in primarily urban environments there are no animals to hunt. Food must be found in storerooms or other buildings, and there is simply not enough to sustain one indefinitely.

Another major change in MPO is the radar, which replaces MGS3's dual radar system (itself a split-in-two version of the radar from earlier games) with a general aureal sensor. Clever players will recognize that this sensor is basically a visualization of the directional mic from past games, showing which direction sound is coming from and how loud it is but nothing else. This makes navigating around MPO's urban environments fairly tricky, as great care must be taken to guess where enemies are based on sound. In true Metal Gear fashion, however, MPO alleviates this anxiety by adopted another special case mechanic from past games and blowing it up into a core game system.

Both MGS2 and 3 allowed players to done disguises at certain key points, which allowed them to walk freely among the enemy provided they did nothing "suspicious" (like, for example, wave a gun around). MPO approximates this mechanic by considering all uniformed ex-enemy soldiers "in disguise" when they are on a mission, blending in with enemies of the same uniform. When playing this way a chameleon icon appears on the screen, indicating your cover is intact. In this state you can walk around at your leisure, explore areas, and find items all without having to sneak. Do something "suspicious" though, like skulk around a corner or crawl into an air vent, and your cover is blown. These tensions are further alleviated by "field data", dots that show up on your map telling you where items and enemies are. This is the exact same data that was procured in MGS3 via interrogation, only now it is gather by dispatching "spies" into the field. Unused recruits can be assigned to several jobs of this sort, including weapon development and medical research. These jobs have various effects on how you perform in the field, making them essential to mission planning.

At its simplest MPO is a game about the tensions and logistics of kidnapping, the way MGS2 was a game about the tensions and logistics of murder.  It's about winning the hearts and minds of the enemy and building your former foes into your own guerrilla army. These logistics, which existing Metal Gear mechanics are reconfigured around, grow out of a theme, this time derived from the overarching Metal Gear mythology. Snake/Big Boss's transformation from a solo operative into a great military leader, which had long been part of the Metal Gear backstory, doesn't just guide the narrative of MPO but the entire game design, a design where every "enemy" is just an ally you haven't made yet. In the next installment, we'll see how this increasing focus on soldier behavior leads to a procedural model of the psychological effects of war.