Defense contractor Lockheed Martin is looking to nearly double its annual production of anti-tank Javelin missiles, though it could take “a couple of years” due to the weapons’ helpfulness in Ukraine.

Javelin missiles have become a key weapon for the Ukrainian military as it defends the country from Russia’s invasion, and as such, the United States has provided Ukrainian forces with more than 1,400 Stinger anti-aircraft systems and 5,500 Javelin anti-armor systems. U.S. and Ukrainian officials are counting on Lockheed Martin, which produces the weapon along with Raytheon, to replenish depleted stockpiles, though it won’t be easy.