Taiwan has plans to build eight submarines, which will be a key part of the island’s strategy of deterrence.

President Tsai Ing-wen launched the vessel – named Haikun, meaning “mythical sea creature” – on Thursday into the harbour of Kaohsiung, Taiwan’s southern port city, where tests of its seaworthiness will be conducted in the coming weeks.

“In the past, a domestic made submarine was considered impossible, but today a submarine designed and built by our countrymen is in front of you,” Tsai said at the ceremony.

If all goes well, the first submarine should be ready for delivery by the end of 2024 with a second planned for completion by 2027.

Why does Taiwan need them?

The first submarine came with a hefty price tag of $1.54bn, but for Taiwan’s government, it is worth the cost to defend the island and its outlying territories from China’s navy.

The submarines could keep China’s navy from encircling Taiwan and cutting the island off from outside resources, a move China would be expected to make if it were to attack or invade the island.

Taiwan’s government also said the submarines could keep China from bypassing the First Island Chain, an imaginary line of defence connecting Taiwan, Japan, the Philippines and Indonesia.

How do they fit into Taiwan’s defence strategy?

The submarines are part of Taiwan’s overall strategy of deterrence.

While its military is substantially smaller than China’s, Taiwan’s aim is to make an attack as difficult as possible so it would be too costly to make it worthwhile.

What kind of submarines are being built?

The government aims to build eight diesel-powered submarines to bulk out Taiwan’s existing fleet of two Dutch-made models from the 1980s and a World War II-era US submarine used only for training.

The new models will come equipped with a Lockheed Martin Corp combat system and US-made MK-48 heavyweight torpedoes.

Why does China want to attack Taiwan?

China’s Communist Party claims Taiwan as a province – although it has never ruled it – and it has not ruled out the use of force to achieve its objective.

Analysts said China’s massive People’s Liberation Army will be capable of invading Taiwan by 2027 although that does not mean it will do so immediately.

Why does Taiwan need to produce its own submarines?

While Taiwan buys many of its weapons and defence systems from the United States, the indigenous submarine programme aims to make Taiwan more self-sufficient.

Taiwan has struggled to obtain key defence technology in the past, particularly for submarines, due to its diplomatic isolation.

Did other countries help Taiwan this time?

Seven countries reportedly provided technology to help Taiwan build its submarine fleet, a sign of how concerned some nations may feel about the prospect of China’s expansion into the Pacific.

The Taiwan Strait, the 180km (117-mile) waterway dividing Taiwan from mainland Asia, is one of the world’s busiest shipping lanes, so a military blockade would have a major global impact.