Taiwan received permission from a Dutch ship-building firm to upgrade and modernize two of its aging submarines, the Ministry of National Defense said.

Taiwan’s navy has two Hai Lung-class submarines, closely modeled after the Dutch Navy’s Zwaardvis-class, that are widely considered antiquated. However, Taiwan required the Dutch firm RH Marine’s consent before any upgrades could be made. The Netherlands and other countries have resisted selling weapons or expertise to Taiwan out of fear of angering the People’s Republic of China, which struggles to enforce a global arms embargo on the island state. After the initial sale of submarines to Taiwan in the 1980s, the Netherlands canceled further planned sales after Beijing objected.

The Hai Lung is a diesel-electric attack submarine, first launched in 1986 and outclassed by China’s more modern models such as the Type 092 SSBN and Type 039A.

The life extension program will cost $12.35 million and keep the Hai Lung and Hai Hu in service through the 2030s, the Asia Times reported the defense ministry as saying on Wednesday, May 23.

RH Marine is set to begin work on combat modernization and systems integration in 2020. Taiwan’s navy also wants to upgrade the submarines’ electronic warfare and combat systems and equip them with U.S.-made long-range heavy torpedoes, although the Chung Shan Institute of Science and Technology may carry out that part, Taiwan News reported.

Beijing has repeatedly vowed to unify Taiwan with the mainland, by military means if necessary. Beijing has also stepped up pressure on Taiwan with military deployments near its shores and by convincing other countries to rescind their recognition of Taiwan, formally called the Republic of China.

Taiwan has had difficulty buying weapons or upgrading its existing arsenals and has developed an indigenous defense industry.

Submarines would play a key role if conflict in the Taiwan Strait were to ever break out, as a cost-effective way of dealing with China’s burgeoning surface fleet. In addition to upgrading its Hai Lung-class submarines, Taiwan also seeks to purchase technology from the United States that would enable an indigenously made submarine, similar to how Taiwan developed its indigenous fighter aircraft, the F-CK-1. The U.S. State Department authorized the sale of submarine technology from American defense companies to Taiwan in April.

On Monday, U.S.-based defense contractor AMS group said the company would open an office in Taipei by the end of the year. Michael Perry, senior vice president of global aftermarket, said the firm would provide spare parts and components for Taiwan’s older weapons systems, Taipei Times reported.