WASHINGTON (AP) — U.S. military contractors need at least three years to replenish stockpiles of three key weapons systems used heavily in the Iran war, according to an analysis released Wednesday, adding to concerns that American forces would have limited firepower in any future conflict with China.

The weapons systems are Tomahawk cruise missiles, which are used to strike targets deep inside enemy territory, and Patriot and THAAD interceptors that defend against incoming missiles and drones.

“The United States has enough munitions for any plausible scenario in the Iran war, but the depleted inventories have created a window of vulnerability for a potential Western Pacific conflict,” the Center for Strategic and International Studies said in its new report, provided to The Associated Press. “The time needed to rebuild those inventories has thus become a major concern.”

China has a stated goal of ensuring its military is capable of taking Taiwan by force if necessary by 2027, which experts see as more aspirational than a hard deadline. But Chinese President Xi Jinping warned this month that if Washington mishandles its relations with the self-governing island, the U.S. and China could end up clashing or even in open conflict.

The analysis by the Washington think tank factors in the Republican Trump administration’s historic $1.5 trillion defense budget proposal for 2027, which significantly accelerates spending on high-end munitions that began under the Democratic Biden administration. While there’s bipartisan agreement in Congress to boost inventories, “the problem today isn’t money; it’s time,” the report said.

“It takes time to expand production capacity and to build these complex systems,” the report said, adding that the window of vulnerability will last “for several years until inventories return to their previous levels and another several years before they get to the levels that war planners desire.”

Although munitions inventories are classified, CSIS said sufficient public information exists in Pentagon budget materials to estimate production timelines.