But six years ago, the retired lieutenant colonel found himself an unlikely addition to the gaming community. He's been the military adviser on all six of the "Call of Duty" games, including "Modern Warfare 2," which set the record for the highest grossing entertainment launch ever. If the defensive perimeter is set up properly or if the soldiers move and sound as they should, he's why.
Keirsey served in the Army for 24 years, fought in the first Persian Gulf war and taught military history at West Point before retiring to do consulting work, teaching leadership to corporate executives. He got involved with "Call of Duty" through a contact he had made consulting -- when he saw the developers working for the first time, he was so impressed by their commitment to their product that he decided to stay.
Keirsey's background as a military historian made him well suited to the historical research required when the games were still set in World War II, as well as their newest title, "Black Ops," which is set in the Cold War. He'd go to Veterans of Foreign Wars reunions and interview veterans to get that "one gritty story" that would make their game real.
"At first these veterans would tell me that they didn't want to have anything to do with a video game," Keirsey told AOL News. "And I'd say, 'Well, then, your story will never be told.' And they'd say, 'Well, OK.'"
Despite the necessity of boiling a historical event down to objectives and checkpoints, war as depicted in "Call of Duty" is far from black and white. In "World at War," the developers made a deliberate attempt to show a darker side of World War II, such as showing cheering Russian soldiers standing above mangled German corpses, or giving the player an order to execute a Japanese prisoner with a bullet to the head.
In one chilling scene from "Modern Warfare," the player controls the guns on an AC-130 gunship, watching the action on the ground through a fuzzy infrared camera, seeing nothing but white flashes and hearing nothing but the calm recitation of a teammate: "Tango down."
The new game, "Call of Duty: Black Ops," will likely follow a similar vein as it moves through the murky waters of deniable conflicts carried out behind enemy lines during the Vietnam War. Maj. John Plaster, author of "SOG: The Secret Wars of America's Commandos in Vietnam," served as another key adviser for the project, giving developer Treyarch recently declassified information about how he and his teammates operated in Cold War clandestine operations.
That darker side has gotten the franchise in trouble before. The "Call of Duty" games have garnered criticism in the past for scenes like the one in "Modern Warfare 2" that allow the player to take part in a terrorist massacre at an airport, as well the broader complaint that making a video game trivializes the sacrifices made by American soldiers, whether they fought in Iraq, Afghanistan or Normandy.
For Keirsey, there's only one group of people that really have the right to make that complaint, and soldiers, for the most part, love "Call of Duty."
When he went to Iraq last year, the soldiers Keirsey talked to couldn't have cared less that he was there advising a general. But as soon as they found out he was involved with "Call of Duty," he was a rock star.
Video game consulting isn't something he ever imagined he'd be doing, but Keirsey hopes that these games at least open the eyes of an otherwise passive demographic group to what war means. With the new game, he hopes that those same people who might not otherwise think about military history will start to wonder about the historical circumstances that produced the tragedy in Vietnam, and, ultimately, how those moral imperatives may play out today.
"In my opinion, the entertainment business appeals to something primitive in man," he said. "At least when we do it in a historical context, we awake the thoughts of the intellectually curious."