"Call of Duty: United Offensive is an expansion pack for the popular first-person shooter computer game, Call of Duty. It was developed by Gray Matter Interactive, with contributions from Pi Studios, and published by Activision.
Since October 13, 2006, the game has also been available to buy on Valve's content delivery platform, Steam.
The game features single-player missions centered around the three major Allied forces of World War II: the United States as Cpl. Scott Riley, the United Kingdom as Sgt. James Doyle and the Soviet Union as Pvt. Yuri Petrenko. The game also includes historical battles, such as the Battle of the Bulge, Battle of Kursk, and the Invasion of Sicily. A minor deviation from the original game is a bombing mission in which the player mans several M2 Browning machine guns. Several new abilities are added to the game as well, including the ability to actually deploy light machine guns, use flamethrowers, to sprint; which makes the character run faster but at the cost of not being able to fire their weapon, and the ability to "cook" grenades (allowing the fuse to burn somewhat before throwing the grenade).
The biggest changes made by United Offensive are in the multiplayer aspect of the game. There are new maps which are much larger than the ones in the original game, new weapons from the single player campaign, an in-game rank system which grants additional bonuses with more points, and vehicles such as tanks and jeeps."
Source: Wikipedia, "Call_of_Duty:_United_Offensive," available under the CC-BY-SA License.