The marines are still fighting to keep the MV-22 project going. The marines need something to replace their 210 CH-46Es (carries two tons of cargo or 14 troops, range of about 300 kilometers.) The MV-22 can carry five tons of cargo, or 24 troops and has an unlimited range because it can refuel in the air. The MV-22 can also fly more than twice as fast as most helicopters because of it's tilt rotor design. But this design feature makes the MV-22 less reliable than existing helicopters. In effect, the marines are willing to take the losses (in people and aircraft) to work out the kinks in this new type of aircraft. Meanwhile, there are other military helicopters that can do the job (CH-47 can carry 12 tons or 33 troops, range of 2,000 kilometers, CH-42 can carry 18 tons or 54 troops, range of 900 kilometers, lift nearly 25,000 pounds and carry 33 troops.) There is a special operations version of the CH-53 (the MH-53) that can refuel in the air. Although it's expensive to keep these older helicopters going, so it the cost of getting the MV-22 ready for prime time.