(NewsNation) — Shoulder-fired Stinger missiles are in demand in Ukraine where they have successfully stopped Russian assaults from the air, but U.S. supplies have shrunk and producing more of the anti-aircraft weapons faces significant hurdles.

Challenges include complications related to ramping up production, reluctance by the United States to redirect valuable manufacturing capacity to decades-old technology, and fears among defense companies that they would be stuck with unwanted arms when the Ukraine war winds down, according to interviews with U.S. officials and defense firms.

While U.S. troops themselves have limited use for the current supply of Stingers — a lightweight, self-contained weapon that can be deployed quickly to defend against helicopters, airplanes, drones and even cruise missiles — the U.S. needs to maintain its supply on hand while it develops the next generation of a “man-portable air defense system.”

Since February, the U.S. has shipped 1,400 Stingers to Ukraine, according to an administration official. But sourcing more will be difficult.

According to a U.S. Department of Defense estimate, the U.S. has sent roughly a quarter of its Stinger missiles. However, the Stinger production line was closed in December 2020, said Pentagon spokesperson Jessica Maxwell.

Since then, Raytheon Technologies won a contract in July 2021 to manufacture more Stingers, but mainly for international governments, according to the U.S. Army. The sole Stinger facility, in Arizona, only produces at a low rate.

The Pentagon has not ordered new Stingers for about 18 years, but has ordered parts or made other efforts to increase its supply. For example, the Army is in the middle of a “service life extension plan” for some of its Stingers that were to become obsolete in 2023 and is extending what the military calls their “useful life” until 2030.

The Pentagon, which has thrown together weekly meetings to discuss surging weapons demand from Eastern Europe, met with a group of eight defense-contractor chief executives in mid-April to discuss the supply of weapons to Ukraine, including the Stinger.

Congress also wants more Stingers, or at least something that can do the same job.

The chairman of the House of Representatives Armed Services Committee, Rep. Adam Smith, wrote Secretary of Defense Lloyd Austin last week and pointed out an “apparent absence of a Department of Defense plan to meet short-range air defense replenishment requirements for not only our U.S. stocks of Stinger systems, but those of other contributing allies and partners.”

A Pentagon official who oversees weapons acquisitions for the Army, Doug Bush, told Congress on March 31 the Defense Department was putting together a plan to increase Stinger production and planned to inform Congress imminently.

But as of late last week, a second congressional source who spoke on condition of anonymity said there has been no information about the plan.

Sen. Richard Blumenthal, a member of the Senate’s Committee on Armed Services, asked Austin earlier in April at a Senate budget hearing about using the Defense Production Act (DPA) to restore depleted supplies of Stingers and Javelin anti-tank missiles.

But using that law, which forces industry to put resources into an immediate effort to make a product needed for national security purposes, is premature, Pentagon spokesperson Jessica Maxwell said.

In the longer term, the Army is looking for a replacement for the Stinger that will go into production in 2027.

Reuters contributed to this report.