In November, 2005, ten U.S. Marines were killed, and eleven wounded, when they walked into an IED (Improvised Explosive Device) ambush near Fallujah, Iraq. This is unusual, because foot patrols are particularly alert to the possibility of IEDs being in the area. The enemy knows they have little chance of success in a shoot out with Americans, and thus prefer to try hitting U.S. troops via what amounts to a remote ambush. While this tactic has a low probability of success, it's more certain, and a lot safer, than a firefight. Troops on foot patrol have been threatened by IEDs before, usually when they repeatedly patrol along the same route, or when one of their waypoints becomes known. The terrorists have bomb planting teams that can work quickly to emplace and camouflage an IED. While air cover (a helicopter or UAV), is often assigned for convoys, foot patrols rarely get it, unless there is a high probability that hostile forces would be in the area. Even then, it's not a sure thing that the UAV will catch the enemy planting the IED. Often, the enemy will plant IEDs at places where patrols often pass. If the enemy has enough resources to plant a lot of IEDs, and risk losing most of them (as is usually the case, because most are spotted and destroyed by U.S. troops), or just gets lucky, they will be able to set an IED off close to a foot patrol. Since these IEDs often use large (152mm) artillery shells, the effect is the same as using heavy artillery on the troops. Infantry in the open (standing up) are very vulnerable to this kind of attack.
The U.S. Marine Corps prefers foot patrols to ones using their standard armored vehicle. This is the AAV-7, which has been involved in incidents where large numbers of troops are killed when the vehicle is hit by a roadside bomb. The problem is the AAV (amphibious armored vehicle) the marines use. The AAV was built to get two dozen marines from the sea, across a beach, and protect the passengers from bullets and shell fragments. The army vehicles (Bradley and Stryker) carry half as many people, and are better able to deal with IEDs (Improvised Explosive Devices).
The marines are building a new amphibious vehicle that is supposed to be better able to deal with blast attacks. Or so goes the theory. Don't know if they have tested any of the pre-production models with IEDs. The marines are trained and equipped for amphibious operations, and this presents them with some additional problems when they get mixed up with something like Iraq. The marines are adaptable, their equipment less so.