The U.S. Army will be forced to cut its artillery production target by more than a quarter if Congress fails to pass the national security supplemental that provides military aid to Ukraine, Taiwan, and Israel as well as weapons to replenish U.S. stockpiles, military officials said on Tuesday.

“Bottom line is that short of the supplement that we will end up hitting a ceiling,” said Maj. Gen. Joe Hilbert, the Army’s director of force development, in a briefing on Tuesday. “Without the supplemental, we will cap out at about 72,000 [rounds] a month.”

A little more than $3 billion of the total $106 billion supplemental request bill—which has been debated over in Congress for nearly five months, although it passed in the Senate in mid-February—would go toward buying more 155 mm artillery shells and building new production facilities, including in California, Virginia, and Tennessee. General Dynamics is planning to open three artillery production lines in Mesquite, Texas, to provide for the growing demand.

In fighting the largest land war in Europe since World War II, Russia has expended between 12 to 17 million rounds of artillery ammunition since its full-scale invasion of Ukraine two years ago; the astronomical rates of fire have been used to dislodge entrenched defenses and spur advances on both sides.

The U.S. defense industrial base has more than doubled its output of 155 mm artillery ammunition since December 2022. U.S. companies are currently producing about 30,000 shells a month, and the Army hopes to increase that tally to 60,000 rounds per month by September 2024, and to 100,000 rounds per month by the end of 2025.

“We’ve got two issues in terms of defense budgets,” said Jeb Nadaner, a former U.S. deputy assistant secretary of defense for industrial policy. “One is the orders you place, in a year’s budget. But the other one is, can the industrial base produce it? And the base is really creaky.”

Artillery is not the only major weapons capability that the Pentagon is hoping to build up. The supplemental also includes plans to boost production for U.S.-made Patriot air defense interceptors to 650 per year, about a 15 percent increase. Ukraine operates a handful of the U.S.-built air defense systems. The supplemental also provides funding for a TNT factory that would provide explosives for artillery rounds and other weapons systems, Gabe Camarillo, the undersecretary of the Army, told reporters earlier in March. The bill also includes $3.4 billion in funding for the flagging U.S. submarine industry.

With no U.S. artillery ammunition arriving in Ukraine since December, Kyiv has tried to build more weapons of its own. The U.S. Army has already awarded contracts to American companies to help assemble and fabricate every piece of a 155 mm round—which, at about 6 inches at the base, includes energetic explosives such as TNT, primers, fuses, artillery charges, propellants to ignite the cannons, and the projectile itself. Ukrainian officials have said that they can fabricate projectiles, and multiple U.S. companies have agreed to produce explosives and propellants on Ukrainian soil, but Ukrainian officials say that Kyiv can’t build charges on its own.

Ukraine has received about 300 artillery weapons capable of firing 155 mm rounds since the start of the war—nearly half of them coming from the United States—ranging from U.S.-made M777 howitzer cannons to French Caesar guns and self-propelled German Panzerhaubitze.

But with rounds supplied by U.S. producers dwindling, European countries are turning to ad hoc solutions to keep Ukrainian guns firing. NATO has signed a $1.2 billion artillery ammunition contract to procure rounds on behalf of Belgium, Lithuania, and Spain. The European Union—which is months late on its target of producing 1 million artillery shells by the start of this month—is hoping to get to 1.4 million shells produced by the end of the year. But short of that, a Czech-led initiative has sought to source 800,000 rounds of artillery ammo from outside the European Union for Ukraine.

And while European officials are confident that they can continue the upward trajectory for artillery ammunition production and other weapons needed to help the Ukrainians, such as air defense projectiles, they insist that they can’t do it without the United States, which has a larger overall defense industrial base.

“We physically don’t have the weapons that are needed at the front,” said Radoslaw Sikorski, Poland’s foreign minister, at a breakfast hosted by the Christian Science Monitor in Washington on Tuesday. If the aid package doesn’t arrive, Sikorski said, NATO’s eastern flank will likely need to be reinforced with more U.S. troops, to head off a possible further westward assault from the Russians.

The United States has also had to turn to accounting tricks. On Tuesday, Pentagon officials said that they had cobbled together a new $300 million military aid package for Ukraine using savings from Army contracts that had run under budget.

Ukraine is down to firing less than 2,000 rounds per day, down from around 6,000 per day last summer. Researchers estimate that Ukraine needs to fire at least 75,000 rounds a month—more than its current rates—to keep up a defensive war. Without enough rounds, U.S. defense officials say, Ukraine could be pushed back.

“Just look at what’s happening on the battlefield today around Avdiivka and other places,” a senior U.S. defense official told reporters on Tuesday, referring to a Ukrainian city that recently fell to Russian forces. “Ukrainians are struggling without ammunition.”

Still, Washington’s artillery shell production goal for the end of next year is less than half of what Russia is producing right now. And Russia’s economy, which has been converted to mobilize for war, is outproducing countries on both sides of the Atlantic Ocean all on its own. CNN reported on Monday that Russia was on track to produce three times more munitions than the United States and Europe combined this year.

And the Biden administration’s massive $850 billion defense budget plan would cut the amount of money that the Pentagon is pledging to build up training grounds and stage U.S. troops on NATO’s eastern flank. Those cuts are due to the U.S. military’s desire to focus on preparations for a future conflict with China, said Maj. Gen. Charles Lombardo, the director of training for the Army’s deputy chief of staff, during a press call on Tuesday.

“China, North Korea, Iran, Russia—they don’t have many problems producing things out of their defense industrial base. They are producing unbelievable quantities,” said Nadaner, the former U.S. defense official. “If you look at the United States and its allies, we can’t produce enough shells, we can’t produce enough ships, we can’t produce enough submarines. The system can’t produce much.”