ZUOYING NAVAL BASE, Taiwan — The Hai Pao, one of Taiwan’s four navy submarines, began its service as the Tusk, a US vessel launched in August 1945 at the end of World War II. Its sister submarine, the Hai Shih, is a year older. Neither can fire torpedoes today, though they can still lay mines.

The submarines, said Feng Shih-kuan, Taiwan’s minister of national defense, “belong in a museum.’’

The Hai Pao will instead remain in service past its 80th birthday, a relic of a military that once was one of Asia’s most formidable.

Taiwan’s aging submarine fleet is but one measure of how far the military balance across the Taiwan Strait has tilted in favor of the island’s rival, mainland China.

A military modernization overseen by the Chinese president, Xi Jinping, whose political power reached new heights after last month’s Communist Party congress in Beijing, has proceeded in leaps and bounds, lifted by hefty budget increases that have made China the world’s No. 2 military spender after the United States, though it is a distant second.

Taiwan’s armed forces, by contrast, have fallen way behind, struggling to recruit enough soldiers and sailors — and to equip those they have.

A major obstacle is that countries that might sell it the most sophisticated weaponry are increasingly reluctant to do so for fear of provoking China, which claims Taiwan as part of its territory. The unwillingness to anger China extends even to the United States, on which Taiwan has long depended for its defense.

This shifting balance affects more than just Taiwan. The Taiwan Strait was once Asia’s most ominous flash point, with the potential to drag the United States into war with China. Now, it is just one of several potential hot spots between a more assertive China and its neighbors.

Taiwan’s experience could be a cautionary tale to Japan, South Korea, Vietnam, and others in the region who are also warily watching China’s rising military capabilities.

In a separate development Saturday, leaders of China’s Communist Party-controlled legislature, the National People’s Congress, passed a law making disrespecting the national anthem a criminal offense punishable by up to three years in prison.

The move comes amid rising nationalist rhetoric from the Communist Party under Xi. After his recent appointment to a second five-year term as party leader, Xi touted a vision of achieving a ‘‘Chinese Dream’’ of a powerful, prosperous nation.

Under the new law, penalties include detention, imprisonment of up to three years, and deprivation of political rights. Such punishments previously applied to the desecration of the national flag and emblem in public.

The anthem, ‘‘March of the Volunteers,’’ has in recent months been a political flashpoint in Hong Kong, where tensions are rising over Beijing’s efforts to assert its authority over the semiautonomous territory.

The People’s Congress also demanded that Hong Kong, where free speech has broader protections, adopt the National Anthem Law, earlier legislation that provides 15 days of detention.

Soccer fans in Hong Kong have booed the anthem when it’s played at games between the home team and teams from China or other countries. Prodemocracy activists and lawmakers fear a national anthem law could be used to undermine freedom of speech.

Adding to the unease over China’s military growth has been uncertainty over US policy under President Trump. As he makes his first visit to Asia, allies and others will look for signals about the depth of the US military commitment to the region.

When he was president-elect, Trump signaled a strong embrace of Taiwan by accepting a congratulatory phone call from its president, Tsai Ing-wen. Since taking office, he has shown more deference to China in hopes of winning its support in the nuclear standoff with North Korea.

When the Trump administration approved a new package of arms sales to Taiwan this summer, it was worth a relatively modest $1.4 billion, less than the $1.8 billion package approved by President Barack Obama two years ago.

Any weakening of the US defense commitment “is what Taiwan worries about most,’’ said Lu Cheng-fu, an assistant professor at National Quemoy University.