In Chain Reaction, there are five hills numbered from 1-5. Each team must capture the hills from one upwards in numerical order.
The hills are represented by a glowing circle with a flame in the middle. The circle's colour changes depending on the hills status. Yellow for neutral, green for when your team have captured it, and red when the opposing team has captured the hill. Hill number one is usually near the team's spawn base, number two a little more far out and number three is always in the center of the map. The more players of the same team in a hill, the faster it is captured. If there are two or more players from opposing teams in one hill, it turns yellow for neutral and will not capture for either team until only one team is in it. If neither team have captured the last hill after 20 minutes is up, the game is considered a tie.
In Uncharted 3, Chain Reaction only appears when playing Team Objective. It has a 50% chance of being first, and if it is not first it will not appear in the game. The objective is the same as it is in Uncharted 2, except now the hills are square and much larger. White is now the neutral colour instead of yellow.
During some previous cash multiplier events, Chain Reaction was removed from all playlists to prevent players using the gametype for boosting.
However, this game mode is now unplayable as people use this game mode for boosting to get loads of cash, due to the game being so old Naughty Dog hasn't done anything about it.