On August 16, US airstrikes in the vicinity of Mosul Dam began. Previously, airstrikes had largely been centered on protecting Erbil, where the US Consulate is located, and some in support of humanitarian relief operations on Sinjar Mt. The limited authorization for strikes “in support of humanitarian operations and to protect US personnel and facilities” pretty much ensured, to begin with, that those were going to be the only targets. Direct support for Peshmerga and Iraqi Army operations against ISIS appeared to be off the table.

However, the strategic significance of Mosul Dam ultimately decided the expansion of US operations. Not only does the dam control power and water for most of northern Iraq, but it is notoriously unstable. Built on gypsum, anhydrite, marl, and limestone, all of which dissolve when exposed to water, the dam requires constant maintenance to keep it from collapsing. There were concerns about Saddam’s loyalists demolishing the dam during the initial invasion in 2003. Worry that ISIS would blow the dam seemed even more urgent. Were the dam to be breached, the flood waters in Mosul itself are estimated to be 65 feet deep. Baghdad would be flooded as well, though not as catastrophically as Mosul. Considering the US personnel still in Baghdad, the administration has announced that securing the dam falls under the mandate of protecting US personnel and facilities. The administration justified the action under the War Powers Act with the following letter, courtesy of the Long War Journal:

On August 14, 2014, I authorized the U.S. Armed Forces to conduct targeted air strikes to support operations by Iraqi forces to recapture the Mosul Dam. These military operations will be limited in their scope and duration as necessary to support the Iraqi forces in their efforts to retake and establish control of this critical infrastructure site, as part of their ongoing campaign against the terrorist group the Islamic State of Iraq and the Levant (ISIL). The failure of the Mosul Dam could threaten the lives of large numbers of civilians, endanger U.S. personnel and facilities, including the U.S. Embassy in Baghdad, and prevent the Iraqi government from providing critical services to the Iraqi populace. Pursuant to this authorization, on the evening of August 15, 2014, U.S. military forces commenced targeted airstrike operations in Iraq.

I have directed these actions, which are in the national security and foreign policy interests of the United States, pursuant to my constitutional authority to conduct U.S. foreign relations and as Commander in Chief and Chief Executive. These actions are being undertaken in coordination with the Iraqi government.

I am providing this report as part of my efforts to keep the Congress fully informed, consistent with the War Powers Resolution (Public Law 93-148). I appreciate the support of the Congress in this action.

Nine strikes were launched on the 16th, hitting armored vehicles and armored personnel carriers. The strikes were launched before the President’s War Powers Resolution letter, so some questions were asked about how they fit into the scheme of “humanitarian aid and protecting US personnel,” as there were no US personnel in the area of Mosul Dam. The next day, more strikes destroyed more ISIS vehicles and a checkpoint. By then, it was obvious that the strikes were in support of Peshmerga and ISOF forces driving on the dam.

By the 17th, the Peshmerga were claiming that the operation to retake the dam was “almost finished.” With approximately 120 ISOF soldiers in support, by the 18th they had pushed into Telsqof and Risala, and from there into the gate complex of the dam. ISIS bombed the bridge south of the dam to slow the Peshmerga advance. Al Jazeera is reporting that while ISIS has been driven out of the dam complex, the dam itself cannot yet be occupied, because ISIS fighters set IEDs throughout before pulling back.

ISIS has vowed retaliation against the US for its involvement, threatening to strike Americans “anywhere.”