ukraine stinger missiles
CNN  — 

As the first full winter of Russia’s war with Ukraine sets in, the US is running low on some high-end weapons systems and ammunition available to transfer to Kyiv, three US officials with direct knowledge tell CNN.

The strain on weapons stockpiles – and the ability of the US industrial base to keep up with demand – is one of the key challenges facing the Biden administration as the US continues to send billions of dollars of weapons to Ukraine to support its fight against Russia. One of the officials said the stockpiles of certain systems are “dwindling” after nearly nine months of sending supplies to Kyiv during the high-intensity war, as there’s “finite amount” of excess stocks which the US has available to send.

Among the weapons systems where there’s particular concern about US stockpiles meeting Ukrainian demands are 155mm artillery ammunition and Stinger anti-aircraft shoulder-fired missiles, the sources said.

Some sources also raised concerns about US production of additional weapons systems, including HARMs anti-radiation missiles, GMLRS surface-to-surface missiles and the portable Javelin anti-tank missiles – although the US has moved to ramp up production for those and other systems.

For the first time in two decades, the US is not directly involved in a conflict after withdrawing from Afghanistan and transitioning to an advisory role in Iraq. Without the need to produce weapons and ammunition for a war, the US has not manufactured the quantities of materiel needed to sustain an enduring, high-intensity conflict.

Defense officials say the crunch is not affecting US readiness, as the weapons sent to Ukraine don’t come out of what the US keeps for its own contingencies.

But the seriousness of the problem is a source of debate within the Defense Department, officials say. While the US will not be able to provide high-end munitions to Ukraine indefinitely, assessing whether the US is “running low” on stockpiles is subjective, one senior defense official said, as it depends on how much risk the Pentagon is willing to take on.

Multiple officials underscored that the US would never put at risk its own readiness, and every shipment is measured against its impact on US strategic reserves and war plans. Both Defense Secretary Lloyd Austin and Chairman of the Joint Chiefs of Staff Gen. Mark Milley monitor levels of US stockpiles closely, officials said.

A major manufacturing challenge

One reason for the concern about low stockpiles is that the US industrial base is having difficulty keeping up with demand quickly enough, the sources said. In addition, European allies cannot sufficiently backfill Ukrainian military requests due to their need to maintain to their own forces’ supplies.

“It’s getting harder and harder,” Rep. Mike Quigley, a member of the House Intelligence Committee, told CNN. “This is a war we thought would be over in days bu