“We’re expending munitions faster than we can replenish them,” USA Today quoted Air Force Chief of Staff Gen. Mark Welsh as saying in December.

Since then Secretary of Defense Ash Carter has asked Congress to include funding for 45,000 smart bombs in the Defense Department’s 2017 budget. But it could take a while to rebuild the stockpile.

“The US maintains a pretty steady inventory of bombs and missiles for full-on war scenarios,” says Roman Schweizer, aerospace and defense policy analyst at Guggenheim Securities in Washington. “But 2 1/2 years of fighting ISIS and continued bombing in Afghanistan have exceeded weapons-use projections.”

Operation Inherent Resolve, the US-led military intervention against the Islamic State of Iraq and the Levant flies bombing missions in Syria and Iraq. The United States, which flies a majority of the missions, strikes ISIS targets with laser- and GPS-guided bombs, Joint Direct Attack Munition bombs, Joint Standoff Weapons, and air-to-ground missiles, such as the Hellfire. Per unit pricetags on these munitions range from around $25,000 to close to $400,000.