for release in the last quarter of 2005. Collier said the request would help them lose the stigma of being only a personal computer developer, and so to make sure the console version was on parity, they tripled their staff to about 75 employees. Much of the focus of Infinity Ward's development was improving its game engine to include realistic special effects, such as smoke grenades to hinder sight, or bullets piercing through weak materials. Call of Duty 2 was a major success, having an 85% attach rate to new Xbox 360 console sales, and selling 1.4 million units its first year. At this point, Activision brought in Treyarch, one of their internal studios, to help develop additional Call of Duty games, with Infinity Ward spending the time and effort to improve the game's engine for one game, and Treyarch using the updated engine to create a new title. Treyarch released the next sequel Call of Duty 3 while Infinity Ward itself developed Call of Duty 4: Modern Warfare, which instead of taking place during World War II, was set in a contemporary period with a fictional conflict between superpowers. At the time of Modern Warfares release, Infinity Ward had more than 100 employees. 2010 employee firings and departures Following the critical and financially successful release of Call of Duty 4: Modern Warfare in 2007, Jason West (president, co-CCO, and CTO) and Vince Zampella (CEO) began contract negotiations with Activision. They promised to deliver Call of Duty: Modern Warfare 2 in 2009, but in exchange asked for extremely large bonuses and creative control of the Call of Duty series. Activision agreed, but added a clause to the contract that should they be fired, the rights to Call of Duty would fall back to Activision. Following the execution of the contract in 2008, Activision began seeking ways to find reason to fire West and Zampella to trigger the new clause. This in turn led to West and Zampella look to means to make Infinity Ward a studio outside of Activision's control. Events came to a head in February 2010 when Activision hired a lawfirm to investigate Infinity Ward. On March 1, 2010, West and Zampella were released by Activision for "insubordination", forfeiting the bonuses they had negotiated. The pair went on to form Respawn Entertainment in April 2010 as an independent studio, through working closely with EA on a yet-announced project.