Normally, the constant attacks on American vehicles passing through Sunni Arab areas in Iraq would shut down traffic. But the U.S. Army and Marines added armor, and additional weapons, to their trucks and hummers, and developed tactics to deal with the ambushes. However, adding a ton of armor and weapons to a hummer, in places where extra weight was not anticipated, has created additional stress on the suspension and engines. Hundreds of hummers have unexpectedly required new engines, a process that takes two mechanics eight hours to accomplish. Many hummers were in need of engine changes after only 1600-3200 kilometers of driving with all that new weight. Design changes were made to hummers last year, so that those being produced now have beefed up engines, transmissions and suspensions that greatly reduces the strain, and need for new engines. The army is also considering using a new diesel engine in the hummer, a 6.5 liter model that would be better able to deal with the extra weight, and further reduce fuel consumption.