As a massively multiplayer online (MMO) third-person shooter spin-off, the gameplay of Front Mission Online differs from the tactical role-playing game entries of the numbered Front Mission titles. Rather than being played out on a grid-based map and using a turn-based structure, battles takes place in real-time on full 3D maps akin to Armored Core. The player controls a mech known as the Wanderpanzer, or wanzer. Players in Online can play alone, or in groups of up to 20 players. The game has built-in support for VoIP, which can be used to communicate with other players.
Game progression in Online works differently from other Front Mission entries. As an MMO, players have complete control over how they want to play the game. When a player creates an account, they will be asked to choose a side to fight for - the Oceania Cooperative Union (O.C.U.) or the United States of the New Continent (U.S.N.). Next, the player must create a character to play as; character creation in Online works similarly to character creation methods found in other MMOs. Once a character has been created, the player can then begin playing the game. There are two modes of play - PvE or PvP. In PvE mode, players do battle against enemies controlled by AI. In PvP mode, players do battle against other players of the game.
The PvE mode of Online is unique in that like the other Front Mission titles, there is a storyline that the player can play through. After the player completes a certain amount of missions, they can participate in military operations, which are a series of missions. These military operations progress the storyline. Furthermore, there are limited-time only operations which are open to all players. Unlike missions, military operations are one-time only events and cannot be replayed. The PvP mode of Online, on the other hand, does not have any story elements. Players pick a battle zone on Huffman Island and fight on it, with the winning side taking control of the zone. Battle zones affect the type of missions that a player can go through in PvE mode. For example, if a U.S.N. military base is captured by O.C.U. forces, U.S.N. players can take a mission to recapture it. Likewise, U.S.N. players can take a mission to defend the base if it was not captured. There are many types of missions, ranging from simple destruction requests to more complex reconnaissance ones.
When a player is not currently involved in a mission or military operation, they are stationed at military bases and supply camps on Huffman Island. In here, they can customize their wanzers, purchase battle gear for their pilots, form groups with other players, or fight other players in the Arena to earn extra money and parts. Players can also defect to the other side if their combat proficiency is at a certain level. Defecting players are demoted by one military rank and lose all of their items, except those that are equipped on their pilot and wanzer. Wanzer customization in Online works differently from other Front Mission titles in that the parts, auxiliary backpacks, and weapons the player can access is entirely dependent on their military ranking. Military rankings work in a progression-based fashion; players must complete missions and military operations to advance in rank. A player can also raise their rank by scoring kills on computer-controlled enemies or players fighting for the other side.
Missions aside, Online boasts other new features as well as returning ones, particularly from Front Mission Series: Gun Hazard and Front Mission Alternative. The game introduces many new auxiliary backpacks and weapon types. A new kind of auxiliary backpack is the stealth backpack; this protects a wanzer from being detected on enemy radar and/or can render the wanzer invisible to the naked eye if an optical stealth backpack is used. The burst bazooka is a bazooka fires multiple bazooka rounds in quick succession; it has a high damage output, but is offset by its slow reload times. There are also hybrid shield/weapons that have both an offensive and a defensive feature. Returning features in Online include remodeling and Cockpit Mode. Once a player has reached a certain rank, they can add upgrades to their parts and weapons to make them more effective. Cockpit Mode, which allows players to control the action in a first-person view, has been expanded to allow for zooming in and zooming out of the battle camera. This allows for precision aiming and shooting, which is ideal for weapons such as sniper rifles and bazookas.
The plot of Front Mission Online takes players from the beginning of the 2nd Huffman Conflict to its end in 2091. Unlike Front Mission, the game's plot covers both the minor and major events that occur during the war, such as the war-ending Operation Eagle Tears (coincidentally, this was also the final military operation, taking place from May 27 to May 31, 2008). Online revolves around four military units that play a major role in the war: the Chasm Owls (O.C.U.), Iron Hearts (O.C.U.), Proud Eagles (U.S.N.), and the 17th Mobile Company (U.S.N.). These four military units influence how the war turns out, from the early stages when the U.S.N. military was winning the war, to the later stages when the O.C.U. military begins using mercenary outfits. Throughout the game's service, players could fight alongside or against characters and groups from Front Mission. Additionally, characters from the other Front Mission entries made appearances in several missions or military operations as either allies or enemies.
These are the recurring characters whose first appearance was in Front Mission: Online. The game takes place from 2090 to 2091.
Ellen Taylor - An O.C.U. officer in the employ of the O.C.U. reconnaissance unit, Chasm Owls. Ellen is deployed to the Mail River border on Huffman Island, and is engaged in espionage and reconnaissance activities against the U.S.N. Ellen also makes an appearance in Front Mission 2089: Border of Madness.
Ernest Miller - A U.S.N. officer involved with the U.S.N. Border Patrol Force. During the outbreak of the 2nd Huffman Conflict, Ernest was assigned to monitoring O.C.U. movements by the Mail River border. Ernest also makes an appearance in Front Mission First.
Yuji Kinoshita - An O.C.U. mechanic working with both the O.C.U. military and its hired mercenaries. Yuji is assigned a post on Huffman Island in 2089 to train new mercenary recruits on wanzer piloting and following O.C.U. military procedures. Yuji also makes an appearance in Front Mission 2089: Border of Madness.