As America ramps up its military campaign against the Islamist terror group, the Air Force is now "expending munitions faster than we can replenish them," Air Force chief of staff General Mark Welsh said.
"B-1s have dropped bombs in record numbers. F-15Es are in the fight because they are able to employ a wide range of weapons and do so with great flexibility. We need the funding in place to ensure we're prepared for the long fight," Welsh said in the statement.
The bombing campaign has left the US Air Force with what an Air Force official described as munitions depot stocks "below our desired objective."
The Air Force has requested additional funding for Hellfire missiles and is developing plans to ramp up weapons production to replenish its stocks more quickly. But replenishing that stock can take "up to four years from time of expenditure to asset resupply," the official told CNN.
"The precision today's wars requires demands the right equipment and capability to achieve desired effects. We need to ensure the necessary funding is in place to not only execute today's wars, but also tomorrow's challenges," the official said.
American pilots have fired weapons in less than half of the nearly 18,000 sorties they have in the first 10 months of 2015, according the latest figures available.
That's up from 2014, when pilots fired their weapons just one third of the time, the report said.