As the U.S. gives away billions of dollars in weapons to Ukraine, it is putting stress on defense contractors as the Pentagon looks to backfill the military’s supply of weapons, The Hill reported. 

President Biden’s trip to a Lockheed Martin facility in Troy, Alabama, highlighted a bipartisan sentiment that making sure the U.S. can maintain its own supplies is as important as ensuring Ukraine can defend itself against Russia. 

But replenishing Washington’s stockpile of weapons will be an uphill battle, as experts warn the defense industry is not primed for a wartime surge in production. 

The U.S. has sent $4.6 billion in security assistance to Ukraine since the beginning of the Biden administration. Of this, the administration has used presidential drawdown authority to provide $3.4 billion in weapons from the Pentagon’s stockpile since September 2021. 

Replenishing the U.S.’s stockpile was one of the main issues that Defense Secretary Lloyd Austin was asked about when he testified before the Senate Appropriations Subcommittee on Defense about his agency’s fiscal 2023 budget request. 

The Pentagon chief said it was “very critical” to ensure that Washington won’t dip below minimum stockage levels for critical munitions. He added that the Pentagon has been encouraging manufacturers to open supply lines to increase production. 

Lockheed Martin CEO James Taiclet said in an event hosted by The Atlantic Council that his company is working to expand productions of weapons that it manufactures. 

In addition to the 5,500 Javelin anti-tank missiles that the U.S. has sent to Ukraine, the company also manufactures the Patriot missile defense system, and parts of the Stinger missile mainly created by Raytheon. 

The defense industry has been faced with some of the same challenges that other industries have amid global supply disruptions.

Biden highlighted the fact that the industry has been impacted by the ongoing shortage of semiconductor chips. He noted that each Javelin missile includes about 200 semiconductors.

But the bigger issue, according to experts, is that the defense industrial base is geared toward producing what the U.S. needs in peacetime. 

Retired Maj. Gen. John Ferrari, a nonresident senior fellow at the American Enterprise Institute (AEI), explained that industry tends to wait for the Pentagon to award contracts to build systems. 

Compounding the problem is that the government has been more interested in divesting from procurement and investing in research and development, which sends a signal to industry not to spend big on legacy systems. 

Mark Cancian, a former Pentagon official who is a senior adviser at the Center for Strategic and International Studies, noted that every weapons system that needs to be backfilled is different.

Some weapons can be ramped up quickly, but other weapons, like the Stinger surface-to-air missiles—the U.S. has sent over 1,400 to Ukraine—are not in production as the Army had been moving to retire the weapon. 

Greg Hayes, the CEO of Raytheon Technologies, which makes the missiles, said that the company won’t be able to ramp up production of the missiles until 2023 due to a redesign and lack of parts. 

All of this comes as the White House and Congress work together to get as many weapons to Ukraine as they can.