The Illinois company said a current field service support contract was renewed by the U.S. Marine Corps Systems Command and work will continue until December 2012.
The contract renewal is worth $134 million.
"I'm proud to say that Navistar will not sell a truck if we can't support it in theater," said Navistar Defense President Archie Massicotte. "Sustainment of our vehicles is key -- especially when vehicle lifecycles may run between 15 to 20 years.
"With our fleet of vehicles now growing beyond 32,000 trucks, fleet support will continue to be a critical piece of our business."
Navistar has more than 600 field service representatives in Afghanistan and the United States. In Afghanistan they tend Navistar's International MaxxPro Mine Resistant Ambush Protected vehicles. The vehicles for transporting troops feature modular armor, V-shaped hulls for deflecting blast effects of mines and improvised explosive devices.
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