Task: Question Generation
Input (English): Passage: The U.S. Marine Corps issued a request for proposals (RFP) in 2013 for its Humvee sustainment modification initiative to upgrade 6,700 expanded capacity vehicles (ECVs). The Marines plan to field the JLTV, but do not have enough funding to completely replace all Humvees, so they decided to continue sustaining their fleet. Key areas of improvement include upgrades to the suspension to reduce the amount of force transferred to the chassis, upgrading the engine and transmission for better fuel efficiency, enhancements to the cooling system to prevent overheating, a central tire inflation system to improve off-road mobility and ride quality, and increased underbody survivability. Testing of upgraded Humvees was to occur in 2014, with production and installation occurring from 2015 through 2018. Older A2 series Humvees make up half the current fleet, and 4,000 are to be disposed of through foreign military sales and transfers. By 2017, the Marines light tactical vehicle fleet is to consist of 3,500 A2 series Humvees, 9,500 ECV Humvees, and 5,000 JLTVs, with 18,000 vehicles in total. Humvees in service with the Marine Corps will be upgraded through 2030. The Marines shelved the Humvee modernization effort in March 2015 due to budget cuts.
Output (English): How many years after the U.S. Marine Corps issued a RFP for its Humvee sustainment modification initiative did testing of upgraded Humvees begin?