China is flying missiles over Taiwan and into Japanese waters, in just another sign that Beijing may be closer to trying a military takeover of Taiwan than most believe. Given how long it takes to build modern warships, the U.S. needs to start building now if it is to have the fleet needed to deter Chinese aggression.

Last year, Adm. Phil Davidson, former commander of the U.S. Indo-Pacific Command, cautioned Congress that China is preparing to move against Taiwan by 2027. That assessment is shared by the current Indo-Pacific commander, the current CIA director, and Mike Pompeo, a former secretary of state and CIA director.

Why 2027? Eyeing negative trends in economic, demographic and regional military balance, Chinese leaders worry that the odds of being able to achieve their long-held goal of conquering Taiwan will fade with each passing year after that.

The Chinese Communist Party promised prosperity in exchange for party dominance. And it delivered decades of breathtaking economic growth … until recently.

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A seemingly endless supply of cheap labor allowed China to become the world’s factory, raking in huge profits. This also enriched the party, which was then able to fund massive military programs and conduct nefarious debt diplomacy to buy access to overseas ports and markets.

But China‘s one-child policy created a looming population crisis, and already its pool of able-bodied workers is shrinking. The regime’s disastrous COVID-zero policies and a looming global recession are further stressing the economy.

Beijing is accused of misreporting economic growth and demographics to present a false picture of strength and resilience. However, this façade will crumble as the population declines, driving up labor costs and halving GDP growth rates by decade’s end. A shrinking population will also inhibit China‘s continuing military expansion.

In 2016, China‘s navy surpassed the U.S. Navy as the largest fleet in the world. The Chinese navy has since continued to grow, while ours has gotten smaller. The Chinese fleet is modern and lethal, with everything from nuclear missile submarines to super carriers.

But most of this fleet will reach its 30-year lifetime at this decade’s end. Then, Beijing will have to decide whether to extend the ships’ service lives or continue its high-capacity shipbuilding program. Demographic and economic pressures will make both options problematic.

Further confounding Chinese military planners are increasingly well-armed neighbors. Japan is on track to break its self-imposed 1% GDP limit on defense spending. The newly created AUKUS pact portends the addition of Australian nuclear submarines to the region. And South Korea, Taiwan and the Philippines have all increased their defense spending past that of many NATO members.

As economic, demographic and military-balance pressures build, effective deterrence of Chinese military adventurism this decade will require several things.

First, the U.S. and its allies must present Chinese President Xi Jinping with an unfavorable military-power balance. Building new ships, planes, and increasing supplies of smart munitions would send an unmistakable message to CCP leaders that success in a Taiwan invasion cannot be assured.

This will not be easy. The U.S. is no longer the arsenal of democracy it once was. Economic and industrial vulnerabilities include: inadequate commercial shipping to sustain a wartime economy, too few logistics ships to sustain military operations and a shipbuilding industry too small to maintain today’s fleet let alone build a larger one.

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Unless we move quickly to address these weaknesses, Chinese leaders may well calculate that they could outlast the U.S. in a long war—if they strike sooner rather than later.

The nation has overcome such weaknesses before, most notably with the Naval Act of 1938 that directed a just-in-time 20% growth of the fleet. That act is credited with preparing the nation for the war in the Pacific.

Second, the U.S. must keep the pressure on Taiwan to keep scaling up its military budget and investing in asymmetric weapons to deter a Chinese invasion.

Finally, the U.S. must continue to sow doubt among senior CCP leadership that they will be able to achieve their political objectives through force. One clear way to do that would be by better positioning and operating U.S. military forces in the region to confound Chinese military planning.

China may well regard this decade as offering a limited strategic window of opportunity for taking Taiwan. Washington has little time to avert disaster and close the current U.S. window of vulnerability. It takes years to build up navies, making now the time to start.