ShelterBox and its partner, ACTED, a French nongovernmental aid agency, have been preparing for weeks to get aid supplies ready so they can respond quickly as the battle unfolds in Mosul

Today marked the start of the battle to take control of Mosul back from the Islamic State group, also known as ISIS. The city is the group's last major stronghold in Iraq. But humanitarian aid agencies have known about the military offensive, giving them an unusual opportunity to prepare for the crisis.

"It is rare for the world to get early warning of a vast human catastrophe," says Chris Warham, chief executive of ShelterBox. "The United Nations High Commissioner for Refugees issued a paper in July saying this would likely be the biggest humanitarian crisis of the year — and we better get prepared."

ShelterBox, Rotary's project partner for disaster relief, and ACTED, a French nongovernmental aid agency, have teams in the city of Irbil in Iraqi Kurdistan, 53 miles (85 km) east of Mosul. They have been working since July to get aid supplies ready so they can respond quickly as the battle unfolds.

"By tomorrow, 650 of the 3,000 tents that have been deployed to Irbil will arrive," says Warham. He estimates that, without the early notice, it would have taken ShelterBox at least two and a half weeks to gather these supplies.

Tens of thousands of people have already been displaced from Mosul and surrounding areas since March. The current round of fighting could last weeks or even months and is certain to raise that number, although it's unknown just how many people remain in Mosul and in which direction they might flee.

"Our aim is to get aid to displaced families as quickly as possible," says Rachel Harvey, operations coordinator at ShelterBox, who is in Irbil. "Giving people shelter and essential items such as a solar lamp, blankets, and a water carrier will allow them a degree of dignity and security to rest and recover."

Existing camps are already near or over capacity, so other possible sites are being readied. But Warham predicts that demand will almost certainly outpace supply, which could force many families to seek shelter outside managed camps in an inhospitable landscape during a season given to storms and below-freezing overnight temperatures.

ACTED and ShelterBox have partnered many times around the world. Most recently they worked together to help people in Haiti, where the deadly force of Hurricane Matthew caused a surge in cholera cases and left thousands homeless.

The Islamic State has controlled Mosul, the oil-rich capital of Nineveh province, since June 2014. Before the invasion, the city was Iraq's second-largest and one of its most diverse.

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