One of the many lessons of the Iraq war is also an old one; you can't do combined arms combat well unless you practice it a lot. Officers coming back from Iraq are complaining about this a lot. Combined arms is having tanks, combat engineers and infantry working closely together, especially in urban fighting. It also means having someone in each combat team trained and able to call in artillery, helicopter and bomber support. In Iraq, there was some time before the invasion began to bring the different parts of the team together and let them practice. But that was enough to scare everyone, when they realized that a lot more practice together was needed. That additional practice was later obtained, under fire. Everyone got real good at working with troops they didn't train with that often. Normally, infantry, tank and engineer battalions spend most of their time training within their battalions. Training with "outsiders" (units from another battalion, especially a different type like tanks or engineers) is done less often. While army training regulations stipulate a certain amount of combined arms training, it takes division and brigade commanders to make an extra effort and insure that there is more of this combined arms practice. Getting the helicopters involved is even more difficult, and the air force is almost impossible to get involved on a regular basis. Yet every time a war comes along, the lack of combined arms training is noted, everyone complaints and nothing is changed. Maybe this time it will be different, but probably not.