The List: New Insurgent Tactics

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Downing Helicopters

Whats new: Coordinated attacks and ambushes. Sunni insurgents are now employing multiple weapons systems in bringing down U.S. choppers. The tactic involves a number of individuals coordinating an attack, firing different types of weaponssurface-to-air missiles, heavy machine guns, rocket-propelled grenades, and unguided rocketssimultaneously in order to confuse U.S. pilots. U.S. and Iraqi forces that then respond to the scene of a downed aircraft encounter ambushes, such as roadside bombs laid in advance.

Effectiveness: Nine U.S. military and civilian helicopters have been downed since January 20, more than all the aircraft brought down in 2006. At least 30 U.S. troops and civilians have died in the crashes.

Why it matters: At the outset of the insurgency, small-arms fire was deemed to be the biggest threat to U.S. choppers, so U.S. military commanders instructed pilots to fly at higher altitudes. But flying higher leaves the choppers vulnerable to weapons with longer trajectories, like surface-to-air missiles. The new coordinated attacks leave choppers vulnerable at any altitude, troubling because U.S. forces eager to avoid dangerous roads increasingly rely on them for transport. It also suggests that insurgents are getting better at anticipating U.S. flight patterns.

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Chlorine Bombs

Whats new: Bombs laced with chlorine gas. In at least three bombings in Baghdad and Ramadi in recent weeks, Sunni insurgents have detonated trucks filled with explosives and canisters of chlorine. In late February, U.S. forces raided a bomb-making factory outside Fallujah where cylinders of the chemical were found.

Effectiveness: Exposure to chlorine, which was commonly used as a weapon in World War I, can be lethal in heavy doses. Even at low levels, it can cause respiratory trouble and skin irritation. Over two dozen people have been killed directly by the actual explosions where the chemical was present, but the gas itself has left several hundred bystanders stricken with exposure symptoms.

Why it matters: Introducing a chemical component to bombs has the potential to create mass panic and casualties in a way that a single explosion never could. There have been just a few instances so far of chlorines use in Iraq, but Evan Kohlmann, a terrorism expert with Globalterroralert.com, warns that the insurgents are adapting quickly: Though chlorine bombs and chemical rocket attacks have limited real impact right now these sorts of innovative tactics could be perfected.

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Direct Attacks on U.S. Bases

Whats new: Brazen attacks on U.S. facilities. Roadside bombs, mortar fire, and snipers have generally been the hallmark of insurgent attacks on U.S. forces. But a few attacks in recent months have been far bolder.

Effectiveness: In January, four U.S. soldiers were kidnapped from their compound in Karbala and killed by insurgents posing as a U.S. security team. The insurgents wore U.S. military fatigues, spoke English, and traveled in black Suburbans. And in February, suicide bombers drove three cars into a U.S. outpost north of Baghdad, killing two and wounding 17 U.S. soldiers. And it isnt simply U.S. facilities that are becoming targets for these brazen attacks. On March 6, dozens of al Qaeda militants stormed an Iraqi jail in Mosul and temporarily freed 140 prisoners, many of them believed to be insurgents.

Why it matters: Insurgents have mostly avoided attacks on major U.S. facilities, relying instead on attacks from a distance. But direct attacks signal a new type of confidence, and they often damage the hard-won trust between U.S. and Iraqi forces. No matter if there is one attack of this nature or 10, you can bet that security measures have changed, says Michael OHanlon, a security expert with the Brookings Institution, and peoples confidence in their Iraqi partners has diminished.

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Explosively Formed Projectiles (EFPs)

Whats new: A dramatic increase in the use of these deadly roadside bombs. EFPs are explosives that launch balls of molten copper capable of tearing through vehicle armor at nearly one mile per second. U.S. military officials say that EFP attacks in 2006 were nearly double what theyd encountered in the previous 18 months.

Effectiveness: Theyve been called perhaps the most feared weapon faced by American and Iraqi troops today. Thats because they can penetrate some of the most armored vehicles the U.S. military has to offer. The casualty rate in EFP attacks tends to be higher than in traditional roadside bombings too. The Pentagon blames the bombs for 170 U.S. troop deaths and more than 600 casualties since 2004.

Why it matters: EFPs have been used against U.S. forces since the beginning of the insurgency, but a dramatic press briefing by U.S. military officials in Baghdad at the end of February put the weapons on the front pages of newspapers. The officials alleged that Iran is providing Shiite militias in Iraq with a deadly arsenal of EFPs. Many security analysts saw the briefing as just another move in the chess game with the Islamic Republic, pointing out that the weapon parts could easily be manufactured in Iraq. No matter the provenance, the possibility that EFPs could become Shiite militias weapon of choice has U.S. military officials extremely troubled.

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