Battlefield is a series of first-person shooter video games developed by Swedish company EA DICE and is published by American company Electronic Arts. It started out on Microsoft Windows and OS X with Battlefield 1942, which was released in 2002. The Battlefield series has been played by more than 50 million players worldwide as of August 2012. The series features a particular focus on large maps, teamwork and combined arms warfare. The PC games in the series are mainly focused on online multiplayer. Gameplay Battlefield series games usually focus on large-scale, online multiplayer battles. Playing in squads has become a major element of games in the series. Apart from soldiers, also tanks, airplanes, and other vehicles may participate in these battles. Since Battlefield 2, the series centrally recorded online stats for each player, allowing users to receive rank promotions and weapon unlocks based on their performance as well as awards such as medals, ribbons, and pins. A class system is present within all the Battlefield games. Each class features a different type of primary weapon along with different equipment, differentiating roles on the battlefield. The ability to engage other players in melee combat with a knife has been present in Battlefield games. Since Battlefield 2142, the series has included an award of dog tags for each player killed using a knife. Since the introduction of Frostbite, almost fully destructible maps have become one of the most well-known features of the series. Games Development history Battlefield 1942 was released on September 10, 2002, using the Refractor game engine, and set in World War II. It introduced the "Conquest" gameplay mode, in which players fought for "control points" throughout the map. Two expansion packs were released. Battlefield Vietnam, released in 2004, moved the setting to the Vietnam War, and was built on an updated Refractor engine with various gameplay improvements, such as the ability to fire personal weapons while seated in vehicles, and visualizing dense foliage. The 2005 release Battlefield 2 takes place in the modern day, depicting a war between the United States and China and the fictional Middle Eastern Coalition (MEC). Despite requiring numerous patches due to a large number of bugs and glitches in the game upon its release, it was a large commercial success, selling more than 2,250,000 copies worldwide, by July 2006. One expansion pack, Special Forces, which added Russia, exclusive missions, and new weapons and gadgets,