In April, U.S. President Joe Biden signed into law a trio of emergency supplemental spending bills, including one focused on the Indo-Pacific that is commonly referred to as the Taiwan aid bill. The new legislation seeks in part to address Taiwan’s roughly $19.7 billion backlog of arms sales from the United States—a hot-button issue given China’s increasingly provocative military activities around Taiwan and the perception among some U.S. analysts that Taiwan is not as much of a priority as Washington claims.

Taiwan relies on the Foreign Military Sales (FMS) program for most of its U.S. weapons acquisitions, which typically requires manufacturing major weapons systems from scratch. All FMS sales above a certain threshold—$14 million in Taiwan’s case—must be notified to Congress, which can vote to block the sale, though it has never successfully done so. The bureaucratic FMS process is relatively slow by design, and some delay between congressional notification and delivery is to be expected. Yet Taiwan often finds itself waiting longer than other countries for the same U.S. weapons.

In June 2017, for example, Congress received notification of a sale to Taiwan of 56 AGM-154C joint standoff weapons—guided bombs that use onboard wings to glide to their targets. The contract to produce the bomb was awarded this February, nearly seven years after the congressional notification. By the time the bombs are expected to be delivered, in March 2028, it will have taken almost 11 years for Taiwan to receive the weapons that it purchased.

Delays such as this may not seem important in peacetime, but they could become dire in the not-so-distant future. The so-called Davidson window, when the U.S. Defense Department believes that China’s military will be ready to attack Taiwan, begins in 2027. Perhaps no munition will be more critical to Taiwan’s self-defense in this scenario than the anti-ship missile, which Taipei would need in large numbers to attack Chinese warships and civilian vessels that could bring an invasion force ashore. Ground-based anti-ship missiles carried by trucks are particularly valuable for Taiwan given their mobility, which makes it harder for China to target them.

In October 2020, Congress received notification of an FMS case for nearly $2.4 billion to deliver 100 truck-mounted Harpoon launchers and 400 missiles to Taiwan, which was followed by a September 2022 deal worth an estimated $355 million for 60 air-launched Harpoons. But it took two and a half years from the initial notification for Washington to award the first contracts for this work. Taiwan will likely receive these Harpoon missiles in tranches, but the weapons won’t be delivered in full until 2030—well after the Davidson window begins.

It is difficult to pinpoint the root cause of Taiwan’s weapons backlog with available data. Congressional notifications of arms sales are easy to find, but other steps in the FMS process are not consistently made public. Simply knowing the dates of the signed Letter and Offer of Acceptance (LOA), contract award, and the initial and final delivery of a particular FMS purchase would provide a more accurate picture of why delays occur. Any future reforms to the process should include transparency measures to help researchers and policymakers identify the sources of backlogs for FMS recipients.

U.S. bureaucracy alone cannot explain why Taiwan waits so much longer than other countries for the same weapons. It’s possible that Taiwan’s internal process for payment could be gumming up the works. Purchases of foreign military equipment must be approved by Taiwan’s Legislative Yuan before an LOA can be signed, meaning that legislative delays could create a ripple effect when finalizing contracts with U.S. companies.

Stress on the U.S. defense industrial base probably exacerbates the backlog, too. The COVID-19 pandemic and Russia’s war in Ukraine shed light on bottlenecks and capacity shortcomings in the industry. This has already played out with Taiwan, which reportedly canceled an FMS case for Paladin self-propelled howitzers in 2022 due to production delays. The problem isn’t going away anytime soon, since many of the munitions in Taiwan’s arms backlog are in high demand from Ukraine and other FMS customers.

However, the recent Taiwan aid bill will make it easier to use the presidential drawdown authority (PDA), which allows Washington to take weapons out of its own military stockpiles and immediately transfer them to a foreign country. Because PDA transfers draw from existing stocks, there is no manufacturing wait time, allowing the United States to deliver more rapid support in times of need.

At first glance, PDA transfers seem to be an attractive option for reducing the size of Taiwan’s backlog. It’s clear that the U.S. government also sees them as such: In late 2022, Congress amended the Foreign Assistance Act to authorize $1 billion per fiscal year for PDA transfers to Taiwan, and the supplemental legislation passed in April allocates $1.9 billion for the Defense Department to replenish any stockpiles of weapons that it sends to Taiwan through PDA for fiscal 2024 and 2025.

But the impact of the new legislation will likely be limited, primarily because PDA does not allow Biden to transfer equipment that the U.S. military does not already have in its stockpiles. The three largest backlogged arms sales by dollar value—all done by the Trump administration and representing $12.4 billion, almost two-thirds of the backlog—consist of equipment that the U.S. military does not possess on hand. The largest of these is for 66 F‑16 Block 70/72 aircraft, valued at $8 billion. The U.S. Air Force operates more than 1,000 F‑16s, but this fleet does not include the variant that Taiwan purchased.

Similarly, the United States does not have any Harpoon coastal defense systems in its stockpile. When Washington announced in June 2022 that it was sending truck-mounted Harpoons to Ukraine, it did so via the Ukraine Security Assistance Initiative instead of PDA because there were no systems available for drawdown. (The United States has also used PDA to aid Ukraine, sending an estimated $23.8 billion of equipment through this method since August 2021.)

Washington might have better luck with Abrams tanks, which make up Taiwan’s third-largest backlogged arms sale at $2 billion. The United States has plenty of Abrams on hand, but the model sold to Taiwan—the M1A2T—has unique subsystems. Taiwan could receive less capable tanks sooner through PDA, but the first tranche of its newly built Abrams tanks are supposed to arrive later this year, so waiting a few more months is probably preferable.

The United States could use PDA transfers to reduce other parts of Taiwan’s arms backlog, but in many instances, Washington would find that its defense industry already has contracts to produce the weapons in question, as is the case for HIMARS rocket artillery launchers, MQ-9B drones, and multiple types of missiles and munitions. If Washington could use PDA to transfer these weapons to Taiwan now instead of waiting for defense industry to finish making new systems, it would raise difficult questions about what happens to those contracts. Would the U.S. military receive the contracted weapons instead of Taiwan? Or would the contracts be canceled?

Theoretically, Taiwan could benefit by double-dipping—getting weapons via PDA transfers in the near term while maintaining contracts to get more of the same weapons in the long term. This would be good for building up its military stockpiles, especially munitions. However, if Taiwan is still waiting for FMS cases to be fulfilled, the size of the arms backlog would not change.

It’s clear that PDA transfers may not be the most effective way to reduce the arms backlog. If deployed smartly, however, they can play a valuable role in moving Taiwan toward an asymmetric defense posture and improving its self-defense capabilities. Asymmetric defense, also known as a so-called porcupine strategy, uses large numbers of smaller, less complex capabilities to counter a stronger opponent. For Taiwan, less costly capabilities such as drones, anti-ship missiles, and surface-to-air missiles could prevent China from achieving the air and sea superiority that it would need to invade the island.

To that end, the United States should emphasize PDA transfers for certain categories of weapons. Taiwan needs more munitions and missiles of all types, but especially ground-based anti-air and anti-ship weapons. It is waiting on several types of missiles, including Patriot interceptors, Harpoons, and Stingers. Munitions are another contender for double-dipping, because Taiwan will inevitably need many reloads, and resupply would be difficult after a conflict begins.

But Taiwan has been hesitant to fully embrace an asymmetric defense strategy, and the balance of the arms backlog favors traditional capabilities. Washington can use PDA transfers to signal the importance of asymmetric defense to Taipei and send relevant capabilities that are not currently sold through the FMS system. Good candidates for such transfers include sea mines; the remote-controlled Navy Marine expeditionary ship interdiction system; and small uncrewed aerial vehicles, such as the RQ‑7, RQ-20, and the Switchblade loitering munition.

The PDA funding in the Taiwan aid bill is not a silver bullet for Taiwan’s arms sale woes. Instead of viewing PDA transfers as a tool for reducing the backlog, policymakers should see them as an instrument for building up stockpiles of munitions and pushing Taiwan toward a more effective and sustainable defense strategy. Presidential drawdown authority could be a good Band-Aid for getting weapons to Taiwan, but fixing the long wait times that Taipei faces will require other solutions.