The American-made Patriot surface-to-air missile system has been a workhorse for Kyiv in defending against Russian attacks.

The US Army plans to spend more than $1.3 billion on Patriot missiles for the fiscal year beginning Oct. 1, and has quietly quadrupled its overall purchase target for the air defense weapon that has proven critical not just for Ukraine but also for US forces in the Middle East.

The United States has about 25% of the Patriot air defense missile stockpiles remaining that are needed for the Pentagon’s military plans, The Guardian reports. According to the outlet, the depletion of the stockpiles led to the suspension of supplies to Ukraine.