LOS ANGELES — Ryan Norwalk cleared his schedule.

Unlike his friends who had class or work, the 26-year-old California State University, Northridge college student was spending Tuesday gunning down foes and building his online notoriety in "Call of Duty: Modern Warfare 2," the highly anticipated, first-person shooter video game developed by Infinity Ward and published by Activision Blizzard Inc.

"I want to get a head start before everyone gets it tomorrow," he said.

Late Monday night, Norwalk was among the fans lined up for the "Modern Warfare 2" launch outside the GameStop in West Hollywood, Calif., one of over 10,000 retail outlets deploying the game at midnight. In the first week, fans worldwide are expected to spend at least half a billion dollars on the follow-up to 2007's "Call of Duty 4: Modern Warfare."

"I'll start playing as soon as I get home," said Frederick Guese, a 24-year-old fan donning black paramilitary gear in line outside the Best Buy in West Los Angeles. "I think the servers will probably go down tonight because everyone will be trying to play multiplayer tonight, so I'll probably start with the single-player campaign before going online."

With a tank and humvee stationed in the parking lot, the Best Buy location where Guese was positioned was transformed for the launch. Developers from Infinity Ward were on hand to sign autographs of the Xbox 360, PlayStation 3 and PC game while attendees chugged "Modern Warfare 2"-themed energy drinks and practiced their shooting skills on game consoles.

Many fans were miffed to learn the title was sold at several GameStop locations ahead of Tuesday's launch. A spokesman for the chain said the decision was made to sell reserved copies early after other retailers unleashed the game early. A spokesman for Activision said the publisher had not given any retailer permission to sell the game before Tuesday.

And there were other flaps in the weeks leading up to the game's launch. Footage leaked last month revealed that a skippable level allows players to open fire on innocent civilians as a terrorist in an airport. Earlier this month, Infinity Ward pulled a viral video promoting the game that featured an acronym that is a derogatory term for gays.

"We've been trying to keep the game under wraps for maximum impact for the players," said Infinity Ward CEO Vince Zampella outside the Best Buy in West Los Angeles. "It's been stressful with little things leaking here and there. With the unveiling finally here, we don't have to worry about that stuff anymore. Now it's about what's going to screw up that we have to fix over the next week."